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DISEASES  OF  ECONOMIC  PLANTS 


THE  MACMILLAN  COMPANY 


MACMILLAN  &  CO.,  Limited 


THE  MACMILLAN  CO.  OF  CANADA,  Ltd. 

TORONTO 


DISEASES 

OF 

ECONOMIC   PLANTS 

BY 

F.    L.    STEVENS,    Ph.D. 

PROFESSOR  OF  PLANT   PATHOLOGY  IN  THE   UNIVERSITY 
OK   ILLINOIS 

AND 

J.  G.  HALL,  M.A. 

FORMERLY  ASSISTANT  IN  VEGETABLE   PATHOLOGY  IN  THE 
NORTH  CAROLINA  AGRICULTURAL  EXPERIMENT  STATION 

REVISED  EDITION  BY  F.  L.  STEVENS 


Npw   fork 
THE  MACMILLAN  COMPANY 

1921 


All  rights  reserved 


COPTRIGHT,  1910  and  1921, 

Bt  the  macmillan  company. 


Set  up  and  electrotyped.    Published  September,  1910. 


Revised  Edition,  January, 


PREFACE 

The  present  edition  of  this  text-book  is  designed  primarily 
for  college  students,  but  it  is  hoped  that  it  may  serve  also 
as  a  useful  handbook  for  others  who  may  wish  to  recognize 
plant  diseases  or  to  apply  treatments.  It  aims  to  give  a 
comprehensive  view  of  the  field  and  its  importance,  with 
diagnostic  symptoms  and  suggested  treatment  of  all  of  the 
more  important  diseases  prevalent  on  the  crop  plants  of  the 
continental  United  States  with  brief  notes  or  mere  mention 
of  those  less  serious.  A  few  of  the  more  important  diseases 
not  of  the  United  States  are  also  discussed  briefly.  Diag- 
nostic characters  are  limited  in  the  descriptions  to  those  that 
may  be  recognized  without  the  aid  of  the  microscope.  For 
further  discussion  of  morbid  histology,  or  of  the  morphology 
of  the  parasites  concerned,  the  reader  is  referred  to  other 
books  on  these  subjects.  Descriptions  and  discussions  of 
treatment  are  as  full  as  the  space  admits  and  the  reader  who 
desires  more  complete  information  is  referred  to  the  pertinent 
literature  cited. 

Since  conditions  are  so  diverse  as  to  geographic  loca- 
tion, climate,  and  soils  the  treatment  here  suggested  must 
be  more  or  less  general.  Crop  growers  should  in  all  cases 
endeavor  to  secure  from  the  nearest  Agricultural  Experi- 
ment Station  the  information  best  applicable  to  local  con- 
ditions. 

The  segregation  of  certain  diseases  under  the  caption 
"Minor  diseases"  is  arbitrary  and  it  is  quite  possible  that 
diseases  here  included  may  locally  or  seasonally  be  of  major 
importance,  and  conversely  that  certain  major  diseases  may 
be  of  but  minor  importance.  The  aim,  however,  is  to  in- 
dicate to  the  student  those  which  in  general  are  less  wide- 
spread or  less  likely  to  be  serious.    Ample  cross  references  are 


'^^S' 


'p'^.'vN 


-I  "Ti  an 


vi  Preface 

given  to  render  the  inforniatiou  more  accessible  and  to  avoid 
repetition. 

The  common  names  selected  are  those  that  are  in  general 
use. 

Diseases  due  to  insects  comjirise  a  group  which  involves 
knowledge  of  the  classification  of  insects  and  of  their  life- 
habits.  Such  diseases  are  set  aside  in  the  special  field  of 
the  Entomologist  and  are  not  here  treated.  The  diseases 
due  to  adverse  inanimate  environmental  conditions,  the 
sickening  of  plants  due  to  lack  of  soil  fertility,  to  excess  of 
some  element,  to  overabundance  or  lack  of  water  or  to  im- 
proper physical  condition  of  soil,  etc.,  are  recognized  as 
properly  belonging  in  the  field  of  Agronomy  and  are  treated 
in  this  book  only  in  exceptional  cases. 

During  the  decade  that  has  elapsed  since  the  publica- 
tion of  the  first  edition  there  have  come  into  prominence 
in  the  United  States  numerous  diseases  at  that  time  un- 
known in  America.  Therefore  the  present  edition  includes 
discussion  of  several  scores  of  diseases  of  major  importance, 
some  of  minor  importance,  as  well  as  many  modifications  of 
treatment  that  did  not  appear  in  the  earlier  edition. 

The  author  desires  to  express  his  especial  thanks  for 
aid  in  the  preparation  of  this  volume  as  follows:  To  R. 
J.  Haskell  of  the  Plant  Disease  Survey  of  the  U.  S.  Depart- 
ment of  Agriculture,  who  has  kindly  read  the  proof  with 
particular  reference  to  the  usage  of  common  and  scientific 
names  and  as  to  the  estimates  of  losses  and  statements 
regarding  geographic  distribution;  to  H.  W.  Anderson  of 
the  University  of  Illinois  for  valuable  aid  in  the  preparation 
of  the  sections  treating  of  fruit  disease;  to  E.  C.  Stakman 
of  the  University  of  Minnesota  in  connection  with  the  cereal 
diseases;  to  G.  L.  Peltier  of  the  Alabama  Experiment 
Station  and  W.  A.  Ruth  of  the  University  of  Illinois  for  the 
preparation  of  special  articles. 

F.  L.  Stevens. 

Urbana,  Illinois, 
August,  1920. 


CONTENTS 


Historical   ..... 

Damage  Caused  by  Plant  Diseases 

Prevention  or  Cure  of  Plant  Diseases 
Methods  of  Prevention 


General  Diseases 

Diseases  of  Special  Crops 

Pomaceous  Fruits     . 

Drupaceous  Fruits   . 

Small  Fruits    . 

Tropical  Fruits 

Vegetable  and  Field  Crops 

Cereals   . 

Cereal  Smuts  in  General 
Cereal  Rusts  in  General 
Anthracnose  of  Cereals 
Special  Diseases  of  Cereals 

Forage  Crops  . 

Fiber  Plants    . 

Trees  and  Timber 
General  Diseases 
Special  Hosts    . 

Ornamental  Plants  . 
General  Diseases 
Special  Diseases 

Fungicides   . 

Spraying  Apparatus 

Soil  Disinfection 

Bibliography 

Index  .... 


DISEASES  OF  ECONOMIC  PLANTS 


DISEASES  OF  ECONOMIC 
J  PLANTS 

HISTORICAL  !•  -•  •-«■  27 

1 

The  science  of  Plant  Disease  or  Phytopathology  was  ir 
its  early  formative  period  between  1853  and  1870,  the 
foundations  being  laid  in  the  pioneer  work  of  Berkeley, 
De  Bary  and  the  Tulasne  brothers  in  establishing  the 
parasitism  of  the  fungi,  and  in  Pasteur's  fundamental  work 
on  Bacteria  and  Spontaneous  Generation. 

To  be  sure  some  of  the  most  conspicuous  diseases  had 
long  been  known  by  sight.  Blight  and  mildew  were  re- 
ferred to  in  both  the  Old  and  the  New  Testament.  Wheat 
rust  was  mentioned  by  Aristotle,  350  b.c.  and  reference 
to  mildew  is  found  in  King  Lear,  Act  III,  Sc.  4.  There 
was  legislation  even  regarding  wheat  rust  as  early  as  1660. 
However,  there  was  little  or  no  real  knowledge  of  plant 
diseases  in  those  times,  beyond  the  fact  that  various  diseases 
existed,  and  this  knowledge  was  shrouded  in  superstition. 

Following  the  pioneer  publications  of  Berkeley,  De  Bary, 
and  the  Tulasne  brothers  came  the  more  complete  treatises 
of  Kuehn  (1858),  Hartig  (1874),  Frank  (1880,  1895),  Sorauer 
(1874,  1886,  1908),  Kirchner  (1890),  Tubeuf  (1894),  Prillieux 
(1895),  Delacroix  (1902,  1908,  1911),  Ward  (1896,  1901, 
1909),  and  others. 

It  was  not  until  1873  that  plant  pathology  became  a 
part  of  instruction  in  botany,  and  not  until  1875  that  special 
courses  in  pathology  were  given  in  any  of  the  schools  of 
Ameiica. 

A  series  of  papers  begun  by  Burrill  in  1873,  another  by 
Farlow  in   1875,   and  other  publications  by  Bessey,   con- 

fWf^TT  iHBRART 


Diseases  of  Economic  Plants 


C.  E.  Bessey,  1845-1915  G.  F.  Atkinson,  1854-1918 


Historical  3 

tributed  to  the  knowledge  of  plant  disease  and  served 
especially  to  awaken  interest  in  the  problems  of,  and  to  at- 
tract students  to,  this  field  of  research. 

In  1879  Burrill,  working  upon  the  blight  of  the  pear  and 
apple,  was  the  first  to  attribute  a  plant  disease  to  bacterial 
origin.  His  work  was  confirmed  and  his  conclusions  more 
fully  established  by  Arthur. 

During  the  seventies,  from  two  or  three  workers  in  this 
field,  the  number  rapidly  grew,  augmented  in  the  middle 
eighties  by  the  introduction  of  plant  pathology  into  the 
Agricultural  Experiment  Stations  and  the  United  States 
Department  of  Agriculture,  until  the  number  of  papers 
pubHshed  in  the  United  States  upon  plant  pathology  be- 
tween 1888  and  1900  is  estimated  at  over  four  thousand. 
While  only  a  few  dozen  plant  diseases  had  been  even  cursorily 
described  in  the  United  States  prior  to  1880,  in  1910  a  total 
of  some  525  diseases,  of  which  more  than  250  were  serious, 
had  been  carefully  investigated  and  the  number  since  that 
date  has  been  greatly  increased. 

Historical  concerning  plant-disease  prevention.^'  ^'^^ 
Though  little  could  be  done  to  devise  rational  methods  of 
combating  plant  diseases  until  their  causes  were  known,  a 
very  few  rule-of-thumb,  empirical  ways  of  meeting  them 
had  been  suggested  in  very  early  days.  As  might  be  ex- 
pected, many  of  the  methods  used  were  valueless.  Thus 
Parkinson  early  in  the  seventeenth  century  advocated  the 
use  of  vinegar  to  prevent  canker  on  trees,  and  Forsyth  in 
1790  gave  the  following  directions  for  making  a  mixture  to 
"cure  disease,  defects,  and  injuries  of  plants."  ^  "Take  one 
bushel  fresh  cow  dung,  one  half  bushel  lime  rubbish  from 
old  buildings,  one  half  bushel  wood  ashes,  one  sixteenth 
bushel  pit  or  river  sand.  The  last  three  are  to  be  sifted  fine 
before  they  are  mixed.  Then  work  them  well  together  with 
a  spade,  and  afterward  with  a  wooden  beater  until  the  stuff 
is  very  smooth,  like  fine  plaster  used  for  the  ceilings  of  rooms." 
Soapsuds  or  urine  was  used  to  make  the  composition  of  the 
consistency  of  plaster  or  paint.    After  being  applied  it  was 


4  Diseases  of  Economic  Plants 

covered  with  a  sifting  of  powder  made  of  "dry  powder  of 
wood  ashes,  mixed  with  the  sixth  part  of  the  same  quantity 
of  the  ashes  of  burnt  bones." 


Fig.  1.  —  Erwin  F.  Smith  of  the  United  States  Department  of 
Agriculture. 

Among  the  early  chaff,  however,  there  were  some  grains 
of  wheat.  Thus  Riedel  in  1751  advised  excision  followed  by 
grafting  wax  for  canker,  and  Robertson  in  1821  said:  "Sulfur 
is  the  only  specific  remedy  that  can  be  named  for  the  treat- 


Historical  5 

ment  of  mildew  on  peaches.  It  should  be  mixed  with  soap- 
suds and  then  applied  by  dashing  it  violently  against  the 
trees  by  means  of  a  rose  syringe;"  thus  advocating  a  rem- 
edy  which,  modified,   is  still  prominent  for   this  class  of 


The  aggressiveness  of  several  plant  diseases  in  Europe 
between  1878  and  1882,  particularly  the  downy-mildew 
upon  the  grape,  which,  al)out  1878,  had  invaded  Europe 


Fig.  2.  —  Millardet,  183S-1902,  father  of  the 
Bordeaux  mixture.  Professor  at  the  Univer- 
sity of  Bordeaux. 

from  America,  stimulated  a  search  in  the  former  country 
for  effective  spraying  mixtiu-es.  Trials  of  many  chemicals 
were  made,  but  it  was  left  to  accident  to  suggest,  and  to 
the  genius  of  Millardet,  of  Bordeaux,  France,  to  perfect, 
the  happy  combination  of  lime  and  bluestone  that  we  now 
know  as  Bordeaux  mixture.  It  was  customary  in  certain 
vineyards  to  sprinkle  a  few  rows  of  grapevines  near  the 
road  with  a  mixture  of  milk  of  lime  and  bluestone  to  give 


6  Diseases  of  Economic  Plants  ■. 

them  a  poisonous  appearance  to  ward  off  depredation  of 
the  hungry  passer-by.  The  vines  so  treated  in  1882  were 
noted  by  PriUieux  and  Millardet  to  be  less  injured  by 
the  mildew  than  were  other  vines,  and  they  ascribed  the 
beneficial  effect  to  its  proper  cause,  the  lime-bluestone 
mixture. 

While  several  investigators  were  engaged  simultaneously 
in  experimenting  with  these  chemicals  upon  the  mildew, 
it  was  Millardet  who  first  planned  and  executed  experi- 
ments and  published  results  which  demonstrated  the  com- 
mercial value  of  the  lime-bluestone  treatment. 

The  first  systematic  applications  of  copper,  and  of  copper 
with  lime  as  a  disease  preventive,  were  made  under  the 
direction  of  Millardet,  August  18,  1883.  In  1884  the  work 
was  repeated,  and  in  1885  Millardet  published  the  first 
directions  for  preparing  Bordeaux  mixture: 

Water 130  liters  (34  gallons) 

Bluestone  .....  8  kilograms  (17.6  pounds) 
Lime  .....       15  kilograms      (33  pounds) 

This  mixture  was  to  be  shaken  upon  the  plants  with  a 
broom. 

Following  this  demonstration  came  the  introduction  of 
an  era,  not  yet  at  an  end,  of  active  experimentation  with 
fungicides,  wet  and  dry,  which  has  already  yielded  results 
of  incalculable  value. 

In  1885  also  appeared  for  the  first  time  the  Ammoniacal 
Copper  Carbonate  proposed  by  Professor  Audoynaud  of 
the  Montpelier  Agricultural  School. 

Saunders,  in  the  Canadian  HortiaiUurist  in  1884,  sug- 
gested the  use  of  several  liquid  spraying  mixtures  for  apple 
scab,  but  little  if  any  liquid  spraying  for  plant  diseases  was 
done  in  America  prior  to  1885. 

In  1885,  from  the  Section  of  Mycology,  Division  of  Bot- 
any, United  States  Department  of  Agriculture,  appeared  an 
article  by  Lamson-Scribner,  giving  directions  for  making 
"the  copper  mixture  of  Gironde,"  the  primitive  Bordeaux 


Historical 


mixture.     In  1886  the  spraying  campaign  may  be  said  to 
have  been  well  started  in  this  country. 

The  disinfection  of  seeds  by  bluestone  was  practiced  first 
with  the  cereals  as  early  as  1807  by  Prevost  of  France,  and 
improved  by  Dreisch  in  1873,  by  the  addition  of  a  limewater 
bath  to  follow  the  bluestone.  In  1887  Jensen  of  Denmark 
improved  upon  these  methods  by  developing  his  hot-water 
treatment,  which  has  since  proved 
of  great  value,  not  so  much  for  its 
primary  use,  in  which  it  has  been 
superseded  by  formalin,  but  owing  to 
its  applicability  to  those  loose  smuts 
which  cannot  be  successfully  treated 
by  surface  disinfection.  Similar  seed 
treatments  have  been  extended  to 
the  potato  by  Bolley,  arid  to  cabbage 
by  Harding. 

The  production,  by  breeding,  of 
new  and  disease-resistant  varieties  is 
one  of  the  latest  and  most  promising 
methods  of  combating  plant  diseases. 
Grapes  resistant  to  Phylloxera  were 
produced  by  Millardet;  cotton,  cow- 
peas,  and  watermelons  resistant  to 
wilt  by  Orton;  cabbage  by  Jones; 
tomato  by  Durst  and  others;  tobacco 
resistant  to  Thielavia  by  Johnson. 

No  small  part  in  the  progress  that 
has  been  made  in  the  prevention  of 
plant  disease  is  due  to  the  improve- 
ment of  appliances,  dusters,  pumps,  nozzles,  etc.,  for  dis- 
tributing the  disinfectants  upon  the  plants.  This  progress  is 
well  illustrated  by  comparing  the  broom  of  Millardet  with 
the  knapsack,  barrel,  or  power  sprayer  of  to-day. 


Fig.  3.  —  An  improved 
brush  for  distributing 
Bordeaux  mixture. 
After  Lodeman. 


8  Diseases  of  Economic  Plants 

Important  Events  in  Plant  Disease  History 

Ancient.     Recognition  of  the  existence  of  plant  diseases  in  early 

Biblical  times. 
1683  The  discovery  of  bacteria.    Loewenhoek. 
1807  The   efficiency   of    copper   against   smut   spores    discussed. 

Prevost. 
1821  The  use  of  sulfur  as  a  fungicide  recommended.     Robertson. 

1845  The  use  of  boiled  sulfur  and  lime  for  mildew  advocated. 

1846  The  studies  of  Rev.  M.  J.  Berkeley. 

1853  The  beginning  of  the  "Morphology  and  Physiology  of  the 

Fungi"  and  the  proof  of  parasitism  of  fungi.    De  Bary. 
1861  The  publication  of  the  first  American  paper  on  plant  pathology. 

Engelmann. 
1860-1864  The  founding  of  bacteriology.    Pasteur. 
1864  The  proof  of  alternation  of  hosts,  heteroecism.    De  Bary. 
1869  The  first  university  publication  in  America  regarding  plant 

pathology.    University  of  Illinois. 
1873  Plant  pathology  taught  incidentally  with  botany  in  America. 

Burrill. 
1875  Plant  pathology  first  taught  as  a  special  subject  in  America. 

Farlow. 
1879-1880  Proof  of  bacterial  disease  in  plants.    Burrill. 
1880  The  discovery  of  the  cyclone  principle  in  nozzles.    Barnard. 
1882  The  beginning  of  "Sylloge  Fungorum."    Saccardo. 

1884  Systematic  introduction  of  plant  pathology  into  American 

Agricultural  Experiment  Station  work.    Arthur. 

1885  The  announcement  of  the  Bordeaux  mixture.    Millardet. 

1885  Organization  of  a  Section  of  Mycology  in  the  Division  of 

Botany,  United  States  Department  of  Agriculture.    Lam- 
son-Scribner. 

1886  Proof  that  mosaic  is  infectious.    Mayer. 

1887  The  hot-water  treatment  for  smut.    Jensen. 

1888  The  introduction  of  formalin  as  a  disinfectant.    Trillat. 
1888  Organization  of  the  State  Agricultural  Experiment  Stations. 
1890  The  beginning  of  pump  improvement  for  spraying. 

1894  Establishment  of  the  fact  that  biologic  races  exist.    Eriksson. 


Historical  9 

1906  The  passage  by  Congress  of  the  Adams  Act. 

1906  The  introduction  of  the  use  of  Hme-sulfur.    Cordle}^ 

1907  EstabUshment  of  the  first  university  department  of  plant 

pathology.    Cornell. 
1909  The  organization  of  the  American  Phytopathological  Society. 
1912  The  passage  by  Congress  of  the  Plant  Quarantine  act. 


DAMAGE  CAUSED  BY  PLANT  DISEASES 

The  crop  grower  often  suffers  much  damage  from  plant 
diseases,  entirely  unconscious  of  the  fact  that  his  crop  is 
affected  by  disease.  Or,  if  the  presence  of  disease  is  recog- 
nized, the  amount  of  damage  is  often  underestimated.  Thus 
the  presence  of  oat  smut  to  the  extent  of  15  or  even  40  per 
cent,  is  sometimes  entirely  overlooked  by  an  otherwise  ob- 
servant man. 

An  attitude  of  willful  disbelief  in  the  prevalence  of  a 
disease  is  often  couched  in  such  terms  as  these:  "I  don't 
see  why  I  must  work  to  protect  my  apples  from  rot.  My 
grandfather  used  to  raise  fine  apples  without  any  attention 
to  these  things." 

It  must  be  recognized  that  plant  diseases  are  with  us; 
that  they  are  increasing  by  importation  from  other  coun- 
tries or  other  states;  that  diseases  formerly  insignificant 
are,  in  many  instances,  becoming  serious;  that  long,  inten- 
sive culture  of  one  crop  in  a  locality  permits  new  diseases 
to  develop.  Diseases  have  many  means  of  dispersal;  on 
seed,  hay,  or  other  produce  shipped  by  mail,  express,  or 
freight;  on  animals;  by  wind;  by  water;  by  birds.  Diseases 
will  continue  to  spread  and  to  increase  in  destructiveness 
until  the  individual  and  the  general  public  are  aroused  to 
such  active  appreciation  that  conditions  of  plant  sanitation 
and  plant  protection  become  much  more  general  and  effective 
than  they  now  are. 

Conspicuous  examples  of  the  advent  of  diseases  in  coun- 
tries where  they  were  before  unknown,  are  afforded  by  the 
following:  grape  powdery-mildew,  native  to  America  and 
first  seen  in  Europe  in  1845;  the  American  gooseberry  mildew, 
first  found  in  Europe  in  1900;  the  potato  late-blight,  native 
to  South  America,  noted  in  Europe  in  1830;  the  asparagus 
rust,  introduced  from  Europe  about  1896;  the  hollyhock 
10 


Damage  Caused  by  Plant  Diseases  11 

rust  introduced  about  1886;  the  white-pine  bhster-rust 
introduced  from  Germany  shortly  pi'ior  to  1906;  the  chestnut 
bark-disease,  introduced  from  the  Orient  about  1904.  Other 
examples  are  cabbage  club-root,  potato-wart,  grape  an- 
thracnose,  grape  black-rob,  the  carnation  rust,  and  citrus 
canker. 

Cases  of  interstate  migration  of  plant  diseases  are  numer- 
ous, ^^^  most  prominent  being,  perhaps,  the  asparagus,  holly- 
hock, carnation,  and  chrysanthemum  rusts,  and  the  pear- 
blight. 

Fungi  introduced  into  new  environment,  into  a  new  con- 
tinent, for  example,  owing  to  the  change  in  biologic  equilib- 
rium, to  the  absence,  perhaps,  of  their  natural  enemies  or  to 
readier  access  to  susceptible  hosts  are  often  much  more  de- 
structive than  in  the  countries  from  which  they  came.  This 
fact  finds  illustration  in  many  of  the  diseases,  mentioned 
above,  notably  so  in  the  case  of  the  chestnut  bark-disease. 

Aside  from  diminishing  the  value  of  the  produce  and  the 
thrift  and  future  productiveness  of  perennials,  as  trees, 
vines,  etc.,  plant  diseases  entail  depreciation  in  the  value 
of  land,  and  in  some  cases  even  occasion  large  loss  of  life. 
Thus  the  famine  in  Ireland  in  1845  is  directly  traceable  to 
the  injury  done  to  the  potato  crop  l^y  the  potato  late-blight. 
The  presence  of  ergot  in  grain  used  as  food  for  cattle  or  man 
results  in  disease  and  death. 

The  presence  in  land  of  the  causal  germ  of  the  melon,- 
cowpea,  cotton  or  tobacco  wilts,  of  onion  smut,  cabbage 
club-root  or  black-rot,  or  of  any  one  of  many  other  soil-borne 
pathogenes  precludes  the  possibility  of  successful  culture 
of  the  susceptible  plant  for  a  long  period  of  years,  perhaps 
forever,  upon  the  soil  in  question.  Such  restriction  may 
prevent  the  raising  of  the  crops  that  are  most  profitable 
in  a  particular  section,  and  in  some  instances  depreciation 
of  50  per  cent  or  more  in  the  market  value  of  land  has  resulted 
from  the  invasion  of  one  of  these  ineradicable  soil  pests. 
Still  more  serious  is  this  kind  of  injury  if  the  crop  in  ques- 
tion is  one  which  requires  large  money  outlay  before  the 


12  Diseases  of  Economic  Plants 

presence  of  the  disease  germs  is  manifest.  In  the  case  of 
Sumatra  tobacco  under  shade,  or  lettuce  grown  under 
canvas,  the  money  expended  to  prepare  for  the  crop  may 
aggregate  from  $700  to  $1000  or  even  more  per  acre  the 
first  year.  The  capture  of  such  acreage  by  the  lettuce 
drop  or  the  tobacco  wilt  is  a  far  more  serious  matter  than 
a  plant  disease  is  usually  considered  to  be. 

The  diseases  which  develop  on  the  product  after  harvest, 
while  in  storage,  are  of  peculiar  destructiveness  since  they 
cause  the  loss  of  a  large  percentage  of  the  finished  agricul- 
tural yield. "*•  '"  Thus  a  large  part  of  the  total  yield  of  sweet 
potatoes  is  lost.  Those  diseases  that  develop  in  transit  entail, 
in  addition  to  the  loss  of  the  product,  also  the  freight  charges 
and  many  hundreds  of  thousands  of  dollars  in  litigation. 

Some  of  the  losses  caused  by  diseases  of  a  few  crops  are 
given  below,  merely  as  illustrative  instances.  The  authority 
is  named  with  each  estimate.  These  losses  are  in  many 
instances  much  larger  than  is  indicated,  due  to  increase  in 
market  value  of  the  product. 

The  California  vine  disease  in  1892,  $10,000,000.  Pierce. 

Wheat  rust  in  the  United  States,  1898,  $67,000,000.  Galloway. 

Wheat  rust  in  Illinois,  1885,  $1,875,000.  Burrill. 

Violet  leaf-spot  in  the  United  States,  1900,  $200,000.  Dorsetf. 

Peach  leaf-curl  in  the  United  States,  1900,  $2,335,000.  Pierce. 

Potato  late-blight  in  New  York,  1904,  $10,000,000.  Stewart. 

Oat  smut  in  the  United  States,  annual,  $6,500,000.  Orton. 

Wheat  loose  smut.  United  States,  annual,  $3,000,000.  Orton. 

Wheat  bunt  in  the  United  States,  annual,  $1 1,000,000.  Orton. 

Potato  blight  in  the  United  States,  annual,  $36,000,000.  Orton. 

Wheat,  1917,  all  diseases,  64,440,000  bu.  Lyman.a 

Oats,  1917,  all  diseases,  153,973,000  bu.  Lyman. 

Corn,  1917,  all  diseases,  175,344,000  bu.  Lyman. 

Potato,  1917,  all  diseases,  117,174,000  bu.  Lyman. 

Sweet  potato,  1917,  all  diseases,  41,707,000  bu.  Lyman. 

Cotton,  1917,  all  diseases,  1,866,000  bales.  Lyman. 


PREVENTION  OR  CURE  OF  PLANT  DISEASES 

The  burden  of  the  efforts  of  the  plant  pathologist  must 
be  directed  toward  methods  of_  pre:tention,  which  are 
here  worth  far  more  than  their  proverbial  ratio,  since, 
owing  to  the  comparatively  small  value  of  the  individ- 
ual among  plants,  treatment  of  a  plant  already  sick  is 
seldom  attempted  except  in  the  case  of  plants  of  ex- 
ceptional value.  Such  value  very  rarely  attaches  to  an- 
nuals or  biennials;  hence  it  is  only  with  perennials, 
valuable  vines,  bushes,  or  trees  that  cure  of  the  in- 
dividual is  attempted,  and  here  only  in  a  few  special 
cases. 

The  science  of  plant  pathology,  barely  antedating  1880, 
is  yet  young.  Several  of  its  founders  in  America  are  living 
and  are  still  vigorous  workers.  In  comparing  this  youthful 
science  with  its  far  more  aged  prototypes,  human  and  vet- 
erinary medicine,  one  is  astonished  at  the  progress  already 
made,  rather  than  abashed  at  the  multitude  of  diseases  as 
yet  unconquered.«» 

Among  all  classes  of  crops  are  diseases,  single  or  many, 
which  have  given  way  to  the  control  of  man,  many  of  them 
diseases  of  great  destructiveness,  yet  which  are  now  prac- 
tically under  the  subjugation  of  the  intelligent,  educated 
crop  producer. 

The  remedies,  with  one  or  two  exceptions,  are  entirely 
the  result  of  patient,  scholarly  investigation,  careful  de- 
duction, followed  by  experimenting,  testing,  and  improving. 
Such  investigation  is  ever  proceeding  with  increasing  ac- 
tivity, and  each  year,  new  or  improved  methods  of  combat 
are  devised,  so  that  the  future  may  with  confidence  be 
relied  upon  to  see  the  subjugation  of  many  of  the  foes  that 
are  as  yet  unconquered. 

13 


14  Diseases  of  Economic  Plants 

Methods  of  Prevention 

All  methods  of  prevention  of  plant  diseases  due  to  par- 
asites aim  at  the  destruction  of  the  causal  organism,  the 
diminution  of  its  numbers,  or  the  strengthening  of  the  crop 
plant  so  as  to  withstand  its  attack.  The  various  methods 
employed  may,  for  convenience,  be  summarized  as  follows: — 

1.  Killing  the  causal  organism  as  it  rests  upon  the  seed. 
—  Examples:  oat  or  wheat  smut,  cal)bagc  black-rot.  For 
this  purpose  the  seeds  (sometimes  cuttings  or  even  whole 
plants  are  similarly  treated)  are  subjected  to  the  action  of 
heat  or  disinfecting  chemicals  long  enough  to  kill  the  causal 
organism,  but  not  long  enough  to  kill  the  seeds.  Chief 
among  such  disinfectants  are :  — 

Formalin  (40  per  cent  formaldehyde). 

Corrosive  sublimate. 

Copper  sulfate,  followed  by  weak  limewater. 

Heat. 

2.  Killing  superficial  fungi  by  applications  upon  the 
green  parts  of  the  plant.  —  Examples:  powdery-mildew 
upon  grape,  gooseljerry,  or  rose.  This  method  is  applicable 
only  with  the  purely  superficial  fungi,  since  internal  para- 
sites cannot  be  so  reached  without  injury  to  the  host  plant 
itself.  It  finds  prominent  application  with  the  powdery- 
mildews.    The  chief  applications  used  are :  — 

Liver  of  sulfur. 
Bordeaux  mixture. 
Ammoniacal  copper  carbonate. 
Sulfur,  or  sulfur  and  lead  arsenate. 
Lime-sulfur. 

3.  Killing  superficial  fungi  hibernating  upon  the  bark  of 
the  dormant  plant  or  plant  supports.  —  Examples:  apple 
hypochnose,  peach  curl.  For  this  purpose  cleansing  sprays, 
often  called  dormant  sprays,  may  be  used.  Since  the  parts 
of  the  host  receiving  the  spray  are  highly  resistant  to  their 
poisonous  action,  the  sprays  thus  employed  may  be  much 


Prevention  or  Cure  of  Plant  Diseases  15 

stronger  than  could  safely  be  used  when  the  plant  is  in 
foliage.    For  this  purpose  use :  — 

Copper  sulfate  with  lime  sufficient  to  color. 
Lime-sulfur  mixtures. 

4.  The  use  of  protective  sprays  or  dusts.  —  Examples: 
grape  })lack-rot,  apple  scab.  A  protective  spray  or  dust  is  one 
applied  to  the  plant  upon  its  bark,  foliage,  or  fruit,  to  kill 
any  offensive  germs  that  may  fall  upon  its  surface,  or  to  pre- 
vent their  growth  upon  or  into  the  plant.  Such  sprays  are 
distinguished  from  the  cleansing  sprays,  which  are  not 
primarily  for  protection  against  future  invasion,  but  rather 
for  the  purpose  of  cleaning  off  or  killing  all  spores  actually 
upon  the  plant.  Protective  applications  are  usuall}^  em- 
ployed when  the  plant  is  in  foliage,  and  therefore  must  be 
used  with  due  regard  to  the  susceptibility  of  the  plant  to 
the  poison  employed.    They  should  be  applied:  — 

1.  Often  enough  to  replace  any  previous  protective  ap- 
plications that  may  have  been  removed  by  rain  or  other 
means. 

2.  To  give  protection  to  any  new  surface  of  twig,  leaf, 
or  fruit  which  has  developed  since  the  last  protective  treat- 
ment was  made. 

The  first  protective  application  should  be  given  as  soon  as 
possible  after  susceptible  surfaces  have  developed,  and 
before  the  attacking  organisms  are  expected  to  make  their 
invasion.  The  time  varies  of  course  with  each  special  crop, 
with  each  disease,  with  the  climatic  relations  and  section 
of  the  country.  Nor  can  any  absolute  rule  be  laid  down 
for  the  use  of  subsequent  protective  applications.  Fre- 
quency of  rain  is  an  important  controlling  factor.  A  fungi- 
cide, if  rained  upon  just  after  it  is  applied  and  before  it  has 
time  to  dry,  is  easily  washed  off. 

New  tissue  and  new  surfaces  develop  every  day;  there- 
fore, theoretically  to  secure  complete  protection,  sprayings 
should  be  very  frequent,  much  more  frequent  than  is  prac- 
ticable.    To  meet  the  needs  occasioned  by  new  growth,  pro- 


16  Diseases  of  Economic  Plants 

tective  sprays  are  usually  given  at  intervals  of  from  ten  to 
fourteen  days,  though  special  rules  must  govern  special  cases. 

The  chief  protective  applications  are :  — 

Bordeaux  mixtui-e,  full  strength  or  weak. 

Ammoniacal  copper  carbonate. 

The  latter  solution  possesses  the  advantage  that  it  does 
not  spot  the  fruit  and  may  therefore  be  used  near  the  period 
of  maturity,  when  the  Bordeaux  mixture,  owing  to  its 
spotting  effect,  would  be  less  desirable. 

Lime-sulfur  mixtures. 

Sulfin-  and  lead  arsenate. 

5.  Excision  of  the  affected  parts.  —  Examples:  Ash 
white-rot.  Excision  is  resorted  to  chiefly  in  the  case  of  trees 
which  from  their  location  or  quality  possess  value  suffi- 
cient to  warrant  the  necessary  outlay  of  labor.  It  is  so 
practiced  as  to  remove  the  diseased  wood  and  sufficient  of 
the  healthy  wood  to  expose  an  entirely  uncontaminated  sur- 
face. The  wounded  surface  is  then  treated  with  an  antiseptic 
such  as  tar  or  carbolineum. 

6.  Removal  and  destruction  of  diseased  twigs,  leaves, 
or  fruit.  —  Examples:  fire-blight,  peach  brown-rot.  The 
removal  and  destruction  of  diseased  parts  diminishes  the 
number  of  bacteria,  spores,  etc.,  that  are  available  to  spread 
the  disease  and  thus  lessens  infection.  Mummified  fruit 
should  be  picked  from  the  plant  or  the  ground  and  destroyed, 
or  it  may  be  removed  by  appropriate  pasturage  by  fowls, 
swine,  etc.  Affected  leaves  in  many  instances  should  be 
similarly  removed.  Blighted  twigs  and  cankers  should  be 
cut  out  when  seen. 

7.  Removal,  in  whole  or  in  part,  of  complementary  hosts. 
—  Examples:  apple  rust,  wheat  rust.  Complementary  hosts 
always  serve  as  multiplying  places  for  the  causal  parasite, 
and  in  some  instances  are  absolutely  essential  to  its  hiberna- 
tion. Such  complementary  hosts  should,  when  practicable, 
be  removed  from  the  immediate  vicinity,  and,  when  possible, 
not  allowed  to  exist  within  considerable  distance,  one  eighth 


Prevention  or  Cure  of  Plant  Diseases  17 

to  one  half  mile,  or  ))ctter  still,  a  greater  distance.  When 
it  is  not  practicable  to  remove  the  host,  the  offending  por- 
tions may  be  cut  away,  e.  g.  in  the  case  of  the  apple  rust 
the  cedar-balls  may  be  removed  from  adjacent  trees. 

8.  Avoidance  of  disease-bearing  material  or  material 
favoring  disease.  —  Infection  may  roach  hay  through  sick 
melon  vines  (melon  wilt),  or  manure  may  be  contaminated 
by  infected  plant  parts  (potato  seal),  cabbage  rot,  melon 
wilt,  etc.).  Soil  may  wash  from  one  field  to  another  and  bear 
disease  with  it  (tobacco  wilt,  melon  wilt,  etc.). 

9.  Prevention  of  wound  infection.  —  Examples:  heart- 
rots,  sap-rots,  cankers,  fruit-rots.  Wound  infection  may 
often  be  avoided  by  care  in  handling  the  plant  so  as  not 
to  wound  it.  In  trees  place  ladders  carefully,  not  roughly, 
among  the  limbs;  avoid  walking  on  limbs  with  nailed  or 
hard  boots,  etc.  Gather  all  fruit,  root-crops,  etc.,  carefully 
to  avoid  breaking  the  skin  or  bruising  the  underljang  tissue. 
In  case  of  removal  of  large  limbs,  coat  the  exposed  wood 
with  paint  or  tar  to  prevent  invasion  by  parasites. 

10.  Avoidance  of  susceptible  varieties ;  selection  of  resist- 
ant varieties.  —  There  is  much  difference  in  the  suscepti- 
bility of  different  varieties  of  plants.  Study  the  different 
varieties  of  the  crop  to  be  raised,  particularly  in  this  regard, 
and  use  those  that  are  most  resistant.  In  case  resistant 
individuals  are  observed  among  sick  plants,  save  their  seed 
carefully  and  test  the  resistance  in  succeeding  years.  In 
this  way  new  and  resistant  varieties  may  be  developed. 

11.  Avoidance  of  disease-infested  localities.  —  This  is  in 
many  cases  imperative  where  the  soil  is  invaded  by  a  germ 
inimical  to  the  growth  of  crops  of  certain  kinds,  as  in  the  case 
of  cabbage  black-rot,  cotton  and  melon  wilt,  etc.  Similarly, 
low  damp  locations  favor  diseases  of  some  crops  (potato  late- 
blight),  and  the  proximity  of  certain  kinds  of  plants  leads  to 
disease  with  others  (apple  rust).  All  this  should  be  con- 
sidered in  the  selection  of  land  for  the  crop. 

•    12.  The  practice    of    crop  rotation.  —  Constant   growth 
of  the  same  crop  in  any  locality  tends  to  increase  the  enemies 


18  Diseases  of  Economic  Plants  ,| 

of  that  crop.     Rotation  breaks  the  continuity  and  hinders  i 

the  multipHcation  of  the  parasite. 

13.  Avoidance  of  practices  that  aid  in  dissemination  of 
the  parasite.  —  Examples:  bean  pod-spot,  tomato  leaf-spot. 
In  certain  instances  the  spore  of  the  causal  fungus  is  trans- 
ferred from  plant  to  plant  most  freely  when  the  host  is  wet. 
To  avoid  picking  or  cultivating  under  such  conditions  is  to 
lessen  the  spread  of  infection.     Similarly  in  the  greenhouse,  < 

surface  watering  may  spread  the  spores.  By  sub-irrigation 
this  may  he  avoided. 

The  importance  of  sanitary  methods  cannot  be  over- 
emphasized and  stress  on  such  methods  rather  than  on  the 
employment  of  specific  treatment  against  disease  is  a  growing 
tendency.     Many   crops  from   their  very  nature  are  but  j 

slightly  amenable  to  direct  treatment;  others  will  not  need  ] 

it  if  they  are  given  surroundings  that  are,  in  general,  sanitary.  | 

Increased  attention  should,  therefore,  be  given  to  soil  condi-  ] 

tion  both  chemical  and  physical,  to  the  fitness  of  the  crop  to 
the  particular  soil  and  climate,  to  water  relations,  to  crop 
rotation,  to  closeness  of  planting,  ventilation,  to  proper  seed 
selection,  and  modes  of  propagation. 


GENERAL   DISEASES 

The  diseases  discussed  t)elow  are  present  upon  so  man}^ 
different  species  of  plants  that  it  would  seem  that  they  are 
almost  indifferent  to  the  nature  of  their  hosts.  They  may, 
therefore,  be  expected  upon  any  kind  of  plant,  and  are  here 
mentioned  so  that  it  will  not  be  necessary  to  discuss  them 
repeatedly  in  succeeding  pages.  Special  reference  is  also 
made  to  them  under  the  hosts  upon  which  they  are  most 
destructive. 

©  Damping-off.  ^"'  ^^'  ^-  —  Seedlings,  cuttings,  and  other 
weak,  soft  plants  which  lack  in  the  vigor  that  affords  them 
natural  protection  against  their  enemies,  are  subject  to  a 
disease  which  has  come  to  be  generally  known  to  gardeners  as 
"damping-off."  Damping-off  is  most  injurious  to  seedlings 
grown  indoors  or  under  crowded  conditions,  but  it  some- 
times occurs  in  the  field.  It  is  particularly  injurious  to 
seedling  trees  in  the  nursery  where  many  young  seedlings  die 
and  disappear,  or  even  die  ])efore  they  come  above  ground. 
The  loss  is  thus  often  90  per  cent  of  the  stand.  Typically 
damping-off  occurs  upon  seedlings  as  a  rot  originating  at  or 
near  the  surface  of  the  ground.  The  decay  at  this  point  so 
weakens  the  stem  that  the  plant  topples  over  or  "damps- 
off."  Subsequently  the  whole  plant  may  decay,  either 
from  the  primary  cause  or  from  secondary  attacks.  A  short 
time  prior  to  the  fall  of  the  plant  the  leaves  may  appear 
sickly,  although  this  sign  is  so  evanescent  that  it  may  not  be 
noted. 

Upon  cuttings  the  toppling  over  does  not,  of  course,  occur, 
but  the  rot  at  the  ground  line  is  of  the  same  nature  as  in 
the  case  of  seedlings,  and  since  the  diseases  in  the  two  cases 
are  of  similar  nature  and  due  to  similar  causes,  they  are 
placed  under  the  same  caption. 

Damping-off  may  be  caused  by  any  one  of  several  species 
19 


20 


Diseases  of  Economic  Plants 


of  fungi,  prominent  among  them  being  Pythium,  Thielavia, 
Corticium,  Fusarium,  Botiytis,  Sclerotinia,  Sclerotium, 
Phoma,  Volutella,  Phytophthora,  Colletotrichuin,  Gloeospo- 


FiG.  4.  —  Stems  of  young  greenhouse  tomato  plants  damped- 
off  frcm  attacks  of  Corticium.    After  Humbert. 


rium.  The  fungus  which  causes  this  condition  maj^  often  be 
seen  as  a  weft  of  mycehum  around  the  base  of  the  diseased 
plant,  or  even  creeping  over  the  ground  to  some  distance. 


General  Diseases  21 

From  its  original  points  of  attack  it  may  spread  rapidly  to 
adjacent  plants,  often  sweeping  the  whole  seed  bed. 

Since  the  growth  of  these  fungi  is  favored  by  moisture 
and  warmth,  the  trouble  may  often  be  checked  or  pre- 
vented by  keeping  the  beds  cool  and  withholding  any  excess 
of  water;  also  by  means  of  adequate  ventilation,  preventing 
the  accumulation  of  a  vapor-laden  atmosphere  around  the 
bases  of  the  plants.  Thick  sowing  should  be  avoided. 
Frequent  stirring  of  the  top  soil  around  the  plants  aids  in 
drying  it  and  may  stop  an  incipient  attack  of  damping-off. 
Organic  matter  in  the  soil  favors  the  growth  of  damping- 
off  fungi,  and  should  be  avoided.  Fresh,  clean  sand  is  best 
for  most  purposes  of  the  seed  bed  and  cutting  bench. 

Soil  known  once  to  have  sustained  damping-off  may  be 
regarded  as  infested  with  the  fungus  which  caused  it.  Such 
soils  should  not  be  used  for  seedlings  or  cuttings  wit!  i)ut 
disinfection.  If  disinfection  is  impracticabL,  the  soil  should 
be  removed,  the  containers  thoroughly  cleansed  with  a 
spray  of  Bordeaux,  bluestone,  or  formalin,  and  new  unin- 
fested  soil  introduced  or,  in  the  case  of  seed  beds,  a  new  site 
selected. 

Stem-rot,  Root-rot  ^^'  ^^  {Corticium  vaguvi  B.  &  C,  Rhizoc- 
tonia). — The  affected  plants  are  usually  attacked  near  the 
soil-line  or  on  the  roots  where  cankers  of  small  or  large  extent 
develop.  These  cankers  vary  in  character  and  color  with  the 
host  and  conditions  so  that  reliable  diagnosis  can  be  made 
only  by  recognition  of  the  fungus  with  a  compound  micro- 
scope. There  appear  very  fine,  cobwebby  threads,  pale  or 
(|ark,  which  are  often  barely  visible  around  the  roots  of  the 
affected  plants  as  they  are  pulled  from  the  ground.  Masses 
of  fungus  threads  (sclerotia),  also  often  occur.  These  are 
black,  irregular  in  shape,  the  size  of  a  pin-head  or  larger. 
Usually  the  fungus  does  not  bear  spores,  but  in  relatively 
rare  instances  sporiferous  regions  develop  encircling  the 
stem. 

This  stem-rot  has  long  been  known  in  Europe,  and  is  now 
found  in  North  and  South  America,  the  West  Indies,  India, 


22 


Diseases  of  Economic  Plants 


and  Australia,  and  may 
be  regarded  as  of  world- 
wide distribution.  The 
first  account  of  it  in 
the  United  States  was 
made  by  Pamrael  in 
1891.  Since  then  nu- 
merous bulletins  deal- 
ing with  it  on  various 
hosts  have  been  pub- 
lished. It  is  quite  in- 
different to  its  hosts, 
embracing  especially 
members  of  the  pink, 
crucifer,  legume,  po- 
tato, and  sunflower 
families  and  in  all  about 
fifty  families  of  plants 
including  conifers  and 
ferns.  Some  165  spe- 
cies and  varieties  of 
host  plants  are  re- 
corded. Among  these, 
the  most  important  in 
America  are :  potato, 
beet,  lettuce,  bean,  cel- 
ery, carrot,  cabbage, 
eggplant,  tomato, 
sweet  potato,  cucum- 
ber, watermelon,  pump- 
kin, squash,  pea,  corn, 
radish,  rhubarb,  alfalfa, 
clover,  buckwheat,  to- 
bacco, cotton,  aster, 
carnation,  violet, 
cherry,  raspberry,  currant,  pine.  If  conditions  favora- 
ble  to  its  attack    obtain,   the    fungus    may   well    be    ex- 


FiG.  5. 


Corticium  on  cabbage. 
Peltier. 


After 


General  Diseases  23 

pected  upon  almost  any  species  of  plant,  so  wide  is  its  range 
of  hosts. 

Soil  disinfection  (p.  460),  when  practicable,  may  be  em- 
ployed; otherwise  general  sanitary  measures,  destruction  of 
Jjifective  refuse,  and  the  use  of  resistant  plants  are  remedial. 
(7/  Southern-blight^^  (Sclerotium  rolfsii  Sacc). — Plants  af- 
fected with  this  disease  lose  color,  wilt,  and  may  die.  The 
fungus  is  found,  usually,  around  the  base  of  the  stem  or  on 
the  roots,  producing  lesions  of  rot,  a  dense  white  mycelial 
mat,  and  large  numbers  of  spherical,  yellow  sclerotia,  closely 
resembling  mustard  seeds,  which  are  diagnostic.  The  causal 
fungus  may  be  recognized  upon  numerous  hosts  particularly 
in  the  Southern  states,  and  as  far  north,  at  least,  as  central 
Illinois.  It  has  been  identified  upon  tomato,  eggplant,  Irish 
potato,  sweet  potato,  beet,  peanut,  pepper,  cauliflower, 
bean,  cowpea,  cabbage,  carrot,  squash,  muskmelon,  water- 
melon, rhubarb,  fig,  cotton,  violet,  hydrangea,  daphne, 
chrysanthemum,  pinks,  bellflower,  morning-glory,  Japanese 
fiber-plant,  grasses,  sugar  cane,  and  several  weeds  and  may 
be  looked  for  on  any  plant.  Treatment  is  the  same  as  for 
stem-rot.  • 

Texas  root-rot  ^^'^  ^"  (Ozonium  omnivorum  Sh.).* — ^  Most 
destructive  to  cotton  (see  p.  346)  this  disease  affects  a  very 
wide  range  of  plants  in  Texas,  California,  Oklahoma,  New 
Mexico,  and  Arizona.  It  has  been  noted  upon  nursery 
stock,  apple,  mulberry,  chinaberry,  hnden,  ash,  quince,  locust, 
Prunus,  hibiscus,  persimmon,  elm,  lime,  maple,  beet,  peanut, 
bean  and  various  legumes,  flax,  cotton,  sweet  potato,  Sida, 
ragweed,  cocklebur,  alfalfa,  and  several  other  plants.  The 
chief  characteristics  are  a  sudden  wilting  or  dying  of  the 
diseased  plant,  or  if  the  main  root  is  not  completely  diseased 
merely  a  slight  yellowing  and  unhealthy  appearance.  The 
roots  of  plants  that  have  recently  died  are  closely  invested 
with  a  cinnamon-buff  felt  of  hyphae,  in  which  strands  are 
conspicuous.    Treatment  is  as  for  stem-rot. 

*  Duggar  believes  the  conidial  stage  to  be  Phymaiotrichum  omnivorum 
(Sh.)  Dug." 


24  Diseases  of  Economic  Plants 

Root-rot  '^'  1^  {Thielavia  basicola  (B.  &  Br.)  Zopf.).  — 
The  roots  of  the  diseased  plants,  especially  the  tips  of  the 
rootlets,  turn  black  and  decay.  Sometimes  the  stem  just 
above  the  roots  is  cracked  and  deformed  and  the  plant  is 
dwarfed.  Damping-off  may  occur  in  seed  beds.  This  root- 
rot  was  first  noted  in  the  United  States  on  tobacco  in  1904 
and  is  now  known  to  be  widely  distributed.  It  is  found  pri- 
marily on  members  of  the  legume,  potato,  and  cucurbit 
families  but  has  been  identified  on  plants  of  fifteen  other 
families  as  well,  including  the  violet,  composite,  crucifer,  and 
mallow  families.  In  all,  something  over  a  hundred  species 
of  host  plants  are  known  to  be  susceptible,  though  to  largely 
differing  degrees.  In  the  case  of  tobacco  alone  the  average 
annual  loss  is  placed  at  millions  of  dollars.  There  appears 
to  be  no  biologic  specialization  and  the  fungus  that  can  affect 
one  crop  can  pass  readily  to  the  others.  For  treatment,  see 
under  Tobacco,  page  253. 
*''  Root-knot,  nematode  galls.-^'  --■  ^^  —  Root  galls,  varying 
from  a  few  millimeters  to  a  centimeter  or  more  in  size  and 
superficially  resembling  the  root  tubercles  of  the  legumes, 
are  common  upon  a  large  variety  of  crops,  causing  large 
field  loss  in  all  but  the  most  northern  states  as  well  as  serious 
injury  in  greenhouses  everywhere.  Plants  badly  affected 
are  dwarfed  and  are  more  susceptible  to  attacks  of  fungi 
than  are  normal  healthy  plants.  Large  indirect  loss  arises 
from  the  fact  that  nematode-infested  soil  often  prohibits  the 
planting  of  certain  profitable  crops.  These  galls  are  due  to  a 
microscopic  eel-worm  (nematode)  which  enters  the  root 
from  the  soil  and  by  irritation  of  the  root  causes  the  gall  to 
develop.  Following  is  a  list  of  the  more  important  highly 
susceptible  plants.  A  complete  list  would  number  over  five 
hundred  hosts.  Field  crops:  alfalfa,  clover,  cotton,  cowpea 
(except  Iron,  Brabham,  and  hybrids  of  Whippoorwill  crossed 
on  Iron),  field  pea,  flax,  pumpkin,  soy  bean,  sugar  beet, 
sugar  cane,  sweet  potato,  tobacco,  vetch.  Ornamental  and 
drug  plants:  begonia,  cineraria,  clematis,  coleus,  dahlia, 
hollyhock,  ginseng,  goldenseal,  peony,  rose,  sweet  pea,  violet. 

FBOfERTY  UBRARY 


General  Diseases 


25 


Truck  crops:  asparagus,  bean,  carrot,  celery,  cucumber, 
eggplant,  garden  beet,  garden  pea,  Irish  potato,  lettuce, 
muskmelon,  okra,  onion,  pepper,  salsify,  spinach,  straw- 
berry, tomato.  Woody  plants:  almond,  catalpa,  cherry, 
European  elm,  fig.  Old  World  grapevine,  mulberry,  peach, 
pecan,  Persian  walnut^  weeping  willow. 


■^ 

1 

''^"^ 

te..., 

-f^*^2^S^^^ 

1^^^-  '^ 

'^^^JLt-"^^ 

^^^^ 

^Bj&,' ^^""-^ 

^j^ 

o^^ 

^ 

^.v^.  , 

Fig.  6.  —  Root-knot  (nematode)  on  salsify. 
Original. 

In  limited  areas  soil  disinfection  (p.  460)  may  be  em- 
ployed. Thorough  cultivation  and  fertilization  induces  the 
roots  of  perennials  to  extend  deeper  into  the  soil,  thus  reach- 
ing below  the  nematode  zone,  affording  at  least  temporary 
alleviation.  Three  years  of  rotation  with  non-susceptible 
crops  as  corn,  timothy,  red-top,  velvet  beans,  resistant 
cowpeas,  barley,  winter  rye,  or  oats  with  care  to  keep  down 
susceptible  weeds  largely  reduces  the  amount  of  soil  infection. 


26  Diseases  of  Economic  Plants 

Certain  varieties  of  cowpeas  (p.  335),  tobacco,  grapes,  figs, 
and  watermelon  show  resistance.  Calcium  cyanamide, 
1,000  to  5,000  pounds  per  acre  applied  several  weeks  be- 
fore planting  and  followed  by  abundant  water,  reduces  the 
number  of  nematodes. 

Hairy-root,  also  due  to  nematodes,  is  discussed  on  p.  162. 

Certain  fungi  as  Penicillium  (Soft-rot  or  Dry-rot)  p.  51, 
Phytophthora  omnivorum,  Sclerotinia  libertiana  (Drop,  Wilt) 
p.  196,  are  so  general  in  their  habits  as  to  be  found  on  almost 
any  host. 

(i^  Disease  due  to  Impure  Air.'-^'  -^  — ■  Plants  are  sensitive  to 
certain  chemical  impurities  of  the  air  and  may  either  be  killed 
or  greatly  retarded  in  growth  by  them.  These  impurities  are 
chiefly  smoke  and  gases  or  solids  resulting  from  industrial 
operations.  The  aerial  emanations  of  smelters  are  of  a 
character  peculiar  to  the  processes  involved  and  of  a  quantity 
to  make  their  effect  apparent  to  considerable  distances.  It 
has  been  clearly  shown  that  even  small  quantities  of  illumi- 
nating gas  or  sulfur  dioxid  are  very  deleterious  in  their 
effect  upon  plants.  So  marked  are  the  effects  upon  vegeta- 
tion that  definite  zones  of  injury  may  be  mapped  in  the 
vicinity  of  large  air-pollution  centers,  the  outer  zone  extending 
to  a  distance  of  from  75  to  100  miles.  Illuminating  gas  es- 
caping from  mains  into  the  air  of  the  soil  frequently  causes 
death  of  trees.  There  is  considerable  difference  in  resistance 
between  different  varieties  of  plants  and  if  the  air  pollution 
cannot  be  abated  the  more  resistant  varieties  should  be 
planted. 

Soil  diseases.-*^  —  A  group  of  plant  diseases  of  special  de- 
structiveness  comprises  those  of  which  the  causal  organism 
resides  in  the  soil  from  year  to  year  ready  to  infect  any 
susceptible  crop  planted  thereon. 

Notorious  among  such  are  the  wilts  of  the  cotton,  tobacco, 
tomato,  cucumber,  muskmelon,  eggplant,  cowpea,  water- 
melon, cabbage,  flax,  sweet  potato  and  potato;  the  club- 
root  of  cabbage  and  other  crucifers;  black-rot  of  similar 
plants;  smut  of  onion.     Other  soil  diseases  are  potato  M'art 


General  Diseases  27 

and  scabs,  beet  scab,  lettuce  drop,  and  numerous  others 
mentioned  on  following  pages  as  well  as  the  general  diseases 
discussed  aljove.  Since  these  diseases  are  similar  in  their 
mode  of  multiplication  and  dissemination  they  are  given 
general  consideration  here. 

The  peculiar  destructiveness  of  these  diseases  is  due 
to  the  fact  that  they  not  only  kill  the  crop,  but  they  also 
prohibit  successful  culture  of  susceptil)le  crops  in  succeeding 
years.  This  crop  limitation,  if  the  crop  in  question  be  an 
important  one,  perhaps  the  only  really  profital^le  one  suited 
to  the  soil  affected,  may  result  in  large  depreciation  in  land 
values. 

It  is  unknown  how  long  the  germs  can  live  in  the  soil 
without  susceptible  host  plants.  That  they  can  live  from 
one  season  to  the  second  season  following  is  certain.  A 
field  slightly  affected  one  year,  if  put  to  a  susceptible  crop 
the  second  year  after,  will  be  even  more  seriously  infested, 
and  the  trouble  will  grow  so  long  as  such  crops  are  cultivated 
with  but  short  intervening  periods.  Many  cases  are  known 
where  a  rest  of  five  and  even  eight  years  does  not  materially 
restore  the  soil  to  normal  condition. 

The  application  of  chemicals  to  the  soil  is  of  value  only 
in  rare  instances,  and  even  then  is  questionable.  No  means 
of  soil  disinfection  applicable  to  fields  is  known.  Land  once 
infested,  therefore,  can  become  again  usable  only  by  eliminat- 
ing the  causal  organisms  by  a  long  system  of  rotation  which 
is  usually  only  partially  effective,  or  by  the  use  of  resistant 
varieties  of  plants,  and  these  in  most  instances  are  not  as  yet 
known  or  do  not  as  yet  exist. 

In  view  of  these  facts  it  is  especially  necessary  to  stress 
the  importance  of  protection  of  soils  against  infestation. 
To  understand  the  means  of  protection  the  modes  of  dis- 
semination must  be  known. 

All  plants  affected  with  these  diseases  harbor  immense 
numbers  of  the  reproductive  parts  of  the  causal  organisms, 
bacteria,  spores,  mycelium,  sclerotia,  etc.  Upon  the  death 
and  disintegration  of  the  host  plant  they  are  liberated  in 


General  Diseases  29 

the  soil,  where  they  are  able  to  live  for  considerable  time, 
frequently  for  3^ears.  The  immensity  of  their  number  in  a 
diseased  plant  is  inconceivable.  Even  a  few  diseased  stems, 
roots,  or  leaves  in  the  field  will  stock  the  soil  thoroughly.  In- 
fected plants,  or  soil  in  which  infected  plants  have  grown,  or 
which  bears  parts  of  infected  plants  can  therefore  convey 
such  contagion  to  new  fields. 

Instances  may  be  cited  where  the  contagion  has  spread 
by  washing  from  higher  to  lower  land;  moreover  contagion 
may  be  carried  by  any  means  which  can  convey  soil  from 
one  field  to  another,  notably  through  tools  which  have 
been  used  on  infested  soil.  Though  apparently  clean,  such 
tools,  if  they  bear  even  minute  particles  of  soil,  may  convey 
hundreds  of  germs  and  thus  start  an  epidemic  in  a  field. 
The  hoofs  of  animals  or  the  feet  of  laborers  may  in  a  similar 
way  bear  disease-laden  soil.  Wind  passing  over  an  infested 
field  may  pick  up  broken  bits  of  sick  plants  or  germ-laden 
soil,  and  convey  these  to  other  fields.  Infestation  by  wind, 
however,  seems  to  be  rare,  possibly  because  of  the  ger- 
micidal action  of  the  sun's  rays  upon  the  surface  layer  of 
soil  upon  which  the  wind  must  act.  If  the  crop  be  one  which 
is  used  for  stock  feed  or  one  which  may  become  mixed  with 
stock  feed,  the  organisms  may  be  spread  widely  through 
manure  which  has  here  become  infested  from  the  feed 
(cf.  watermelon,  cabbage). 

A  field  may  be  protected  from  higher  land  that  is  in- 
fested by  proper  arrangement  of  dykes.  In  some  cases  a 
thorough  cleansing  of  tools  so  that  there  is  no  possibility 
of  conveying  the  germs  will  aid  in  repression.  The  dirt  may 
be  knocked  off,  then  wiped  off,  and  the  implement  finally 
disinfected  with  a  solution  of  2  per  cent  fonnalin  or  5  per 
cent  carbolic  acid.  It  is  difficult  to  insure  complete  protec- 
tion against  disease  dissemination  by  the  feet  of  animals  and 
man,  but  if  uninfested  land  remains  to  be  protected,  every 
precaution  should  be  exercised  in  this  particular. 

Where  but  a  few  plants  in  a  field  are  affected,  they  should 
be  removed  from  the  soil  and  destroyed  by  fire,  —  root. 


30  Diseases  of  Economic  Plants 

branch,  and  leaf.  Prompt  action  here  may  materially 
lessen  the  rapidity  of  spread  of  the  disease  in  the  field. 
Every  particle  of  the  sick  j)lant  burned  means  the  destruc- 
tion of  millions  of  the  causal  organisms. 

A  long  rotation  of  crops,  one  that  will  bring  the  suscep- 
tible plant  l:)ack  upon  the  affected  field  only  after  an  inter- 
vening period  of  several  years,  perhaps  after  a  period  of 
eight  or  ten  years,  is  useful  in  some  cases,  notably  with 
tobacco  wilt  and  onion  smut,  though  in  other  cases,  notably 
watermelon  wilt,  such  rotation  is  of  little  avail. 

The  one  means  of  overcoming  these  soil  diseases,  which 
is  most  promising  to  farmers,  lies  in  the  discovery  of  a  variety 
of  the  crop  plant  that  will  not  succumb  to  attack  even  when 
planted  upon  infected  soil.  Varieties  of  cotton,  tobacco, 
tomatoes,  cabbage,  flax,  cowpeas,  and  watermelon  that  are 
resistant  to  their  respective  soil  diseases  have  been  dis- 
covered or  developed  by  lireeding.  There  is  similar  hope  in 
regard  to  other  crops. 


DISEASES   OF  SPECIAL   CROPS 

POMACF]OUS  FRUITS  ^s 

The  pomaceous  fruit  plants,  owing  to  the  fact  that  they 
are  long-lived  perennials,  that  their  products  are  standard  and 
of  high  value,  that  they  are  universally  grown  throughout  the 
United  States,  when  subject  to  an  injurious  disease  justify 


Fig.  S.  —  Apple  bitter-rot  in  early  stages  showing  acerviili. 
After  Scott. 

careful  consideration  of  the  means  of  combating  the  disease 
and  the  employment  of  even  expensive  methods  to  attain 
the  end. 

APPLE 

-^Bitter-rot  -^"^•'^     (Glomerella  cingulata  (Stonem.)  S.  &  v.  S., 

Glceosporiuni) .    The  effect  of  the  disease  is  seen  upon  both 

the  fruit  and  the  twig.     Upon  the  fruit  the  rotten  spot  is 

31 


32 


Diseases  of  Economic  Plants 


at  first  soft  and  wet,  in  later  stages  corky,  more  or  less  dry, 
and  brown,  tan-colored,  or  black.  This  spot  under  favorable 
conditions  increases  in  diameter  at  a  rate  vaiying  from  1- 
10  mm.  each  day.  Single  or  numerous  lesions  may  appear 
upon  the  fruit,  depending  upon  the  abundance  of  the  infect- 
ing spores  and  their  ability  to  gain  access  through  the  cuticle. 
When  a  spot  becomes  quite  large,  it  is  usually  somewhat  de- 
pressed, with  a  shriveled, 
wrinkled  surface,  due  to 
loss  of  turgor  of  the  un- 
derlying tissue  caused  by 
evaporation.  As  the  spot 
ages  minute  spore-bear- 
ing pustules  of  the  causal 
fungus,  barely  visible  to 
the  naked  eye,  appear, 
first  at  or  near  the  center. 
The  tissue  of  the  fruit  is 
affected  to  some  depth, 
although  the  progress  of 
the  disease  is  not  so  rapid 
downward  as  laterally. 
The  pulp  of  the  apple  at 
the  margin  of  the  rotten 
region  is  usually  bitter,  thus  giving  rise  to  the  common 
name  of  the  disease. 

Fruit  of  any  age  after  its  formation  is  liable  to  infection 
if  suitable  climatic  conditions  and  infective  material  obtain, 
though  the  disease  is  most  noticeable  and  does  most  damage 
as  the  fruit  approaches  maturity.  A  series  of  hot,  wet  days 
favors  a  destructive  attack,  while  cold  checks  it.  The  fruit 
as  soon  as  it  is  badly  rotted  usually  falls  from  the  tree, 
covering  the  ground  beneath,  while  apples  less  advanced  in 
disease  still  hang  upon  the  limbs. 

This  same  disease  occasionally  affects  twigs  and  young 
branches,  causing  cankers  or  rough  spots  in  the  bark.  Young 
cankers  are  slightly  rough,  owing  to  the  dead  bark,  and  ex- 


FiG.  9.  —  Apple  in  advanced  stage  of 
bitter-rot.    After  Scott. 


Pomaceous  Fruits 


33 


tend  only  partly  around  the  twigs.  Old  cankers  are  very 
rough,  and  may  extend  several  centimeters  longitudinally 
along  the  twig,  thus  giving  it  a  flattened  appearance. 


Pt^^ 


Fig.  10.  —  Bitter-rot  cankers.    After  U.  S.  Dept.  Agr. 


The  fungus  causing  the  rot  upon  the  fruit  was  described 
in  1856  by  Berkeley.  That  the  cankers  are  caused  by  the 
same  fungus  was  recognized  independently  by  two  research 
parties,  Burrill  and  Blair,  and  von  Schrenk  and  Spaulding 


34  Diseases  of  Economic  Plants 

in  1902.  Upon  both  twigs  and  fruit  the  spores  are  borne 
in  great  numbers.  The  fungus  is,  moreover,  perennial 
upon  the  twigs,  the  cankers  serving  as  initial  points  of  in- 
fection for  each  year's  epidemic. 

The  natural  course  of  the  disease  is  through  twig  infec- 
tion ;  spores  from  some  older  lesion  are  transferred  to  points 
of  weakness  on  the  twig,  such  as  bark  ruptured  from  any 
cause.  The  fungus  may  also  develop  and  overwinter  in  old 
cankers  caused  by  other  fungi,  on  dead  twigs  or  scars  on  the 
fruit  spurs,  or  even  in  the  crevices  in  the  bark  and  at  these 
points  produce  spores  the  following  year.  These  in  turn, 
carried  chiefly  by  rain,  partly  by  insects,  possibly  birds,  or 
other  agencies,  fall  upon  apples,  and  there  initiate  spots  of 
rot.  Apples  thus  infected  serve  as  multiplying  ground  for 
the  further  infection  of  other  apples.  Six  days  after  an  apple 
is  infected  a  crop  of  spores  may  mature  and  be  ready  to 
further  spread  the  disease.  To  some  extent  the  causal  fungus 
hibernates  in  mummified  fruits,  which  thus  become  sources 
of  initial  infection  in  the  succeeding  year. 

Bitter-rot  occurs  throughout  the  United  States  wherever 
apples  grow,  but  has  been  most  destructive  heretofore  in 
sections  southwest  of  Virginia  between  the  parallels  of  35° 
and  39°  north  latitude.  It  is  known  also  in  comparatively 
harmless  form  in  Europe  and  Australia.  In  1900  it  was  esti- 
mated that  the  loss  in  four  counties  of  Illinois  was  $1,500,000. 
The  president  of  the  National  Apple  Shippers  Association 
estimated  the  damage  to  the  apple  crop  of  the  United  States 
that  year  as  $10,000,000.  There  is  often  a  loss  of  from  50  to 
75  per  cent  of  the  crop. 

Two  modes  of  treatment  are  useful :  first,  to  cut  off  and 
burn  the  cankers  in  so  far  as  is  practicable,  and  to  hand-pick 
and  destroy  mummified  fruit;  second,  to  spray  the  growing 
fruit  with  a  fungicide.  The  trees  should  be  sprayed  fre- 
quently with  Bordeaux  mixture,  or  lime-sulfur  (summer 
strength)  from  the  time  the  petals  fall  until  the  fruit  is  almost 
ripe.  A  non-spotting  spray  should  be  used  for  the  last 
application.    Cf.  p.  447. 


Pomarcous  Fruits 


35 


J?Scab  ■'^^'  ^■''  '"^^  (Venturia  incequalis  (Cke.)  Wint.,  Fusicla- 
dium).  —  This  is  justly  called  the  most  injurious  disease  with 
which  the  apple  grower  has  to  contend.    Originally  imported 


from  abroad,  the  first  record  is  in  Europe,  1819.  Later  it 
was  noted  in  America,  both  in  New  York  and  Penns3dvania, 
in  1834,  whence  it  apparently  spread  westward.     It  affects 


36 


Diseases  of  Economic  Plants 


both  fruit  and  leaves,  probably  in  all  localities  where  apples 
are  grown,  and  is  serious  in  Europe,  Australia,  Africa,  and 
New  Zealand,  as  well  as  in  Ainerica. 

Upon  the  fruit,  the  scab  first  causes  the  skin  to  take  on 
a  dark  olive-green  color;  later,  as  the  outer  skin  breaks  and 


^^ 

IP 

*i 

9| 

.  1 

^ 

V 

^^V|  '^m 

1 

y 

■ 

Fici.  12.  —  Apple  scab.    After  Craig. 

exposes  the  fungus  underneath,  the  color  changes  to  black. 
An  apple  in  this  stage  is  shown  in  Fig.  12.  Still  later  the 
scab  enlarges,  and  the  spores  and  fungous  cells  at  the  center 
of  the  spot  may  fall  away,  leaving  a  skin  of  rusty  appearance 
surrounded  l^y  a  dark  ring  where  the  fungus  has  not  yet 
fallen  off.  Farther  from  the  center  of  the  spot  may  be  an 
olive-green  or  silvery  ring,  showing  the  still  younger  stage  of 
the  disease.    Cracking  and  distortion  occur  in  cases  of  very 


Pomaceous  Fruits 


37 


badly  affected  fruits.  Scabby  fruits  are  much  more  sus- 
ceptible to  storage  rots  than  are  clean  fruits  (p.  49). 

Upon  the  leaves  and  more  rarely  upon  twigs  the  fungus 
forms  a  thick  velvety  coat,  varying  from  dark  olive-green  to 
black,  in  spots  at  first  circular  in  outline,  later  irregular  and 
coalescing.  The  irritation  and  retardation  of  growth  caused 
by  the  presence  of  the  fungus  often  induces  the  leaves  to  curl 
and  wrinkle  in  a  characteristic  manner.  The  fungus  winters 
on  fallen  leaves,  and  wind-borne  spores  from  them  give  rise  to 
spring  infection.    Cf.  pp.  58,  GO. 

The  injuries  by  this  disease  may  be  enumerated  as  fol- 
lows: lessened  leaf  value,  retarded  twig  and  wood  growth, 
premature  fall  of  fruit, 
retardation  of  full  de- 
velopment of  fruit,  and 
injury  to  sale  and  keep- 
ing quality  of  fruit. 

Baldwin,  Golden  Rus- 
set, and  Hubbardston 
are  among  the  most  re- 
sistant varieties,  though 
scab-resistance  seems  to 
vary  geographically  and 
even  seasonally.  Cf. 
p.  60. 

Bordeaux  mixture  and 
lime-sulfur  are  effective 
sprays.  It  is  especially 
important  to  apply  the 
mixture  immediately  l)e- 
fore  the  blossoms  open,  again  just  after  the  petals  fall,  fol- 
lowed by  one  or  two  later  sprayings.  Cf.  p.  57.  Dusting  is 
discussed  on  page  446.  Burning  of  infected,  fallen  leaves  is 
a  good  sanitary  measure. 

OBlotch  ^^-^^'  ^-^  {Phyllostida  solitaria  E.  &  E.).  —  In  some 
sections  of  the  country  this  disease  of  bark,  leaf,  and  fruit  is 
even  more  troublesome  than  any  of  the  preceding,  though  its 


Fig.  13. 


Apple  blotch, 
and  Rorer. 


After  Scott 


38  Diseases  of  Economic  Plants 

distinct  identity  was  not  recognized  until  1895.  Since  then 
the  disease  has  been  observed  in  the  Eastern  and  South- 
eastern states,  though  not  in 
serious  form.  Its  most  destructive 
center,  heretofore,  has  been  in  the 
Ozarks  of  Arkansas  and  Missouri 
and  in  southern  Ilhnois,  Ohio,  and 
Indiana  where  a  large  per  cent  of 
the  crop  is  commonly  rendered 
unfit  for  barreling.  One  county 
alone  in  Arkansas  is  estimated  to 
have  suffered  a  loss  of  $950,000  in 
1906.  Owing  to  its  superficial 
similarity,  blotch  has  been  con- 
founded with  scab  in  some  in- 
stances. The  first  publication  con- 
cerning the  disease  appeared  in 
1902,  and  the  first  detailed  de- 
scription in  1907. 

Upon  fruit  the  blotches  are  from 
5-20  mm.  in  diameter,  dark  in 
color,  with  an  advancing  margin 
of  peculiar,  irregular,  jagged,  or 
fringed  appearance.  By  coales- 
cence large  spots  may  form,  and 
owing  to  tension,  cracks  appear, 
enlarging  to  a  centimeter  in  length, 
or  even  girdling  the  fruit,  and 
reaching  to  the  core.    In  the  older 

„      , .        .     ,    , ,  ^  1  portions    of    the    blotch,    minute 

Fig.  14.  —  Apple  blotch  on      '         -i-      i        i  t^u        i  i   +  i, 

twigs.    Original.  pycmdia  develop.    These  blotches 

mar  the  appearance  of  the  fruit 
and  injure  it  as  a  salable  product. 

Upon  twigs,  spurs,  or  shoots  are  produced  cankers,  which, 
during  the  first  year,  consist  of  small  spots  2-10  mm.  in 
diameter,  tan-colored,  each  bearing  several  pycnidia.  The 
margins  of  the  spots  are  sharply  limited,  and  are  usually 


Pomaceous  Fruits 


39 


bordered  with  a  narrow  red  line.  In  older  cankers  the 
diseased  bark  becomes  cracked,  furrowed,  and  much  rough- 
ened. 

On  the  leaf  this  fungus  causes  small,  regular,  light  brown, 
yellowish,    or    whitish    spots, 
usually  1-2  mm.  in  diameter, 
each  of  which  may  bear  one 
or  several  pycnidia. 

The  Ben  Davis,  Missouri 
Pippin,  Limber  Twig,  and 
Maiden  Blush  are  highly  sus- 
ceptible, while  Winesap,  Jona- 
than, and  York  Imperial  are 
almost  immune. 

Ordinarily  three  applica- 
tions of  3-4-50  Bordeaux 
mixture  suffice  to  control 
blotch.  The  first  spraying 
should  be  made  two  or  three 
weeks  after  the  petals  have 
fallen;  the  second  about  two 
weeks  later;  the  third  two 
weeks  thereafter.  Lime-sulfur 
should  be  substituted  during 
wet  weather  to  avoid  Bor- 
deaux injury.  Careful  prun- 
ing to  remove  affected  twigs 
is  beneficial. 

QRusts  ^^'  ^^'  ^^^  {Gijmnospor- 
angium  sps.,  Rcestelia). — 
Rusts  of  the  apple  may  usually 
be  recognized  by  their  char- 
acteristic spots  on  the  leaf,  or  more  rarely  upon  the  fruit  or 
twig.  These  spots,  yellowish  green  at  first,  gradually  become 
darker,  approaching  orange.  Upon  close  examination,  the 
upper  surface  of  one  of  these  discolored  spots  is  seen  to  con- 
tain numerous  pustules,  at  first  honey  yellow,  finally  black, 


Fig.   15.  —  Apple    leaf    affected 
with  rust.    After  Anderson. 


40  Diseases  of  Economic  Plants 

smaller  than  a  pinhole,  while  upon  the  lower  surface  of  the 
diseased  spot  appear  some  weeks  later  the  fringe-toothed 
cluster-cups.  This  spot  is  sometimes  so  abundant  that  its 
presence  upon  orchards  may  be  recognized  at  great  distances 
by  the  characteristic  hue  imparted  to  the  foliage  mass  as  a 
whole.  Rust  robs  the  tree  of  nourishment  and  renders  normal 
fruitage  impossible. 

A  peculiar  relation  exists,  in  that  the  causal  fungus  spends 
part  of  its  life  on  one  plant,  the  apple,  and  the  remainder 
upon  a  totally  different  plant,  the  red  cedar  ( Juniperus) ,  the 
Alternate  Host  of  the  apple  rust.  The  fungus  summers  upon 
the  cultivated  apple  or  the  wild  crab-apple  tree,  from  which 
later  spores  are  borne  by  the  wind  to  adjacent  juniper  or 
red  cedar  trees.  There  the  fungus  grows  and  causes  the 
familiar  "cedar  apple." 

In  the  spring  the  cedar  apple  produces  gelatinous,  horn- 
like projections,  each  bearing  myriads  of  spores,  which, 
when  conveyed  by  the  wind  to  the  susceptible  apple  tree, 
under  suitable  conditions,  cause  the  apple  rust.  Evidence 
that  this  relation  really  exists  is  readily  found  if  one  ex- 
amines an  orchard  having  red  cedar  trees  upon  its  windward 
boundary. 

It  is  clear  that  the  more  red  cedar  trees  there  are  in  the 
neighborhood  of  an  orchard,  especially  to  windward,  the 
more  probability  there  is  of  damage  from  the  rust.  The 
rational  treatment,  therefore,  is  to  remove  these  trees  in 
so  far  as  possible,  or  if  the  value  of  the  cedar  warrants  it  to 
hand-pick  the  cedar  galls. 

In  rare  instances  spores  may  be  carried  several  miles,  but 
orchards  are  reasonably  secure  if  all  possibility  of  infection 
from  the  immediate  neighborhood  be  removed;  that  is  to 
say,  for  a  radius  of  two  miles.  In  case  the  red  cedars  are  too 
numerous,  or  if  for  other  reasons  it  is  impossible  to  cut  them, 
spraying  the  apple  trees  at  a  time  corresponding  with  the 
spore  discharge  from  the  cedar-galls  will  lessen  the  evil,  but 
the  success  of  spraying  is  neither  complete  nor  certain. 

Resistant  apple  varieties  are :  Yellow  Transparent,  Maiden 


Pomaceous  Fruits 


41 


Blush,  Baldwin,  Grimes,  Stayman,  Winesap.  The  following 
are  more  susceptible:  Wealthy,  Jonathan,  Rome,  York 
Imperial,  Ben  Davis,  Greening. 

Q  Fire-blight  ■^^  (Bacillus  amylovorus  (Burr.)  Trev.).  —  De- 
scription and  discussion  of  this  disease  will  be  found  on 


Fig 


16.  —  A  cedar  apple  in  condition  to  give  off  spores. 
After  Anderson. 


page  62  under  pear,  the  blight  of  which  is  identical  with  the 
apple  disease.  Its  character  and  treatment  are  the  same  upon 
both  hosts.  While  the  blight  is  preeminently  a  pear  disease, 
it  also  affects  the  apple  very  seriously,  particularly  in  the 
form  of  blossom-blight  and  body-blight. 


42 


Diseases  of  Economic  Plants 


The  Lowell,  Isham,  Smith  Cider,  Yellow  Transparent, 
Jonathan,  and  Willow  Twig  are  especially  susceptible 
varieties,  while  Celestia,  Buckingham,  Mammoth  Black 
Twig,  White  Winter  Pearmain,  Winesap,  and  Ben  Davis 
are  resistant,  the  last  almost  en- 
tii-ely  so.  In  general  the  crab  vari- 
eties are  more  susceptible  than 
others. 

'  ^  Black-rot,  canker  ^^^  ^^  {Physalo- 
spora  cydonice  Arn.,  Sphceropsis) . — 
In  many  respects  this  disease  closely 
resembles  the  bitter-rot,  particu- 
larly in  that  it  appears  both  as  rot 
of  the  fruit  and  as  cankers  upon 
the  limbs.  In  some  instances  it 
also  appears  as  a  twig  blight  and 
as  a  leaf  spot.  As  seen  under  the 
hand  lens  the  coils  of  exuding 
spores  are  black,  instead  of  pink, 
as  is  the  case  with  bitter-rot.  A 
compound  microscope  is  necessary 
to  bring  out  other  distinguishing 
characters. 

The  limb  cankers,  first  studied 
by  Paddock,  consist  of  sweUings, 
with  the  bark  rough,  and  black. 
In  other  cases  the  black,  decayed 
wood  from  which  the  bark  has  dis- 
appeared is  exposed.  This  cankerous  infection  sometimes  ex- 
tends for  nearly  a  meter  along  the  branch,  and  occasionally 
girdles  it.  When  occurring  upon  the  trunk  or  main  branches 
it  is  called  black-rot  body-blight. 

The  Tolman  Sweet  is  said  to  be  quite  resistant  to  canker, 
while  Twenty  Ounce  is  very  susceptible.  Four  other  va- 
rieties range  in  susceptibility  as  follows:  Baldwin,  Wagener, 
Greening,  King. 

Black-rot  twig-blight  somewhat  resembles  fire-blight  with 


Fig.  17.  —  Apple  black-rot 
canker  showing  numer- 
ous pycnidia.  After 
Whetzel. 


Poniaceous  Fruits 


43 


which  it  is  often  associated,  l)ut  may  be  distinguished 
from  it  by  the  presence  of  myriads  of  minute  pimples 
distributed  thickly  over  the  affected  region.  With  a  hand 
lens  coils  of  spores  may  often  be  clearly  seen  issuing 
from  these  pustules. 

Upon  the  leaf, 
blighted  spots  are 
produced,  irregularly 
circular  in  outline, 
often  marked  by 
concentric  rings. 
The  body  of  the 
spot  is  brownish  and 
the  margin  sharply 
limited.  Similar 
spots  are  caused  in 
several  other  dis- 
eases, and  definite 
knowledge  of  the 
nature  of  leaf  spots 
must  depend  upon 
microscopic  diagno- 
sis in  each  special 
case. 

The  various  forms 
of  this  disease  which 
have  been  noted 
above  are  found  in 
Nebraska,.  Michi- 
gan, the  Ozarks, 
Ohio,  Wisconsin,  and 

throughout  the  Allegheny  and  eastern  apple  sections,  and 
are  troublesome  each  year. 

The  treatment  should  be  the  same  as  that  recommended 
for  bitter-rot  with  special  care  to  avoid  bark  wounds  of 
all  kinds,  as  from  ladders  and  workmen's  boots. 

A  rot  upon  fruit  very  similar  to  bitter-rot,  and  a  twig- 


FiG.  18. 


Pacific  coast  canker.    After 
Cordley. 


44  Diseases  of  Economic  Plants 

blight  very  similar  to  that  of  black-rot,  though  less  important, 
is  caused  by  Coniothyrium  fuckelii  Sacc.'*'' 

Pacific  coast  canker  ''^'  ^^  {Neofabroea  malicorticis  (Cord.) 
Jack.,  Gloeosporiuin) .  —  The  Pacific  coast  canker,  first  noted 
about  1893,  is  particularly  destructive  in  the  Northwestern 
states  and  British  Columbia  west  of  the  Cascade  Mountains. 

The  bark  or  sapwood  of  twigs  and  larger  branches  is  the 
seat  of  infection,  but  the  disease  may  occur  also  upon  the 
fruit  when  in  storage.  The  loss  of  an  entire  orchard  within  a 
few  years  has  resulted.  Young  trees,  owing  to  their  tender 
bark,  are  especially  susceptible. 

Upon  twigs,  cankers  in  the  early  stage  appear  as  round  or 
oval,  slightly  sunken,  dark  areas  which  increase  but  slowly 
in  diameter.  As  soon,  however,  as  the  fungus  penetrates 
into  the  cambium  and  sapwood  the  canker  enlarges  very 
rapidly,  making  its  most  rapid  development  through  the 
cambium,  and  advancing  more  tardily  through  the  overlying 
bark.  The  resulting  spots  are  nearly  circular,  quite  black, 
and  from  5  mm.  to  12-14  cm.  in  diameter.  When  old,  the 
bark  becomes  brittle  and  a  definite  fissure  separates  the  dead 
from  the  healthy  portions,  indicating  cessation  of  advance  of 
the  fungus.  The  diseased  bark  eventually  falls  away,  leaving 
a  scar.  Branches,  or  even  trees,  may  be  killed  by  girdling 
cankers. 

Upon  stored  fruit  the  disease  appears  first  as  light-brown, 
circular,  rotten  spots.  These  later  turn  very  dark  or  black, 
and  become  depressed,  dry,  and  tough.  Acervuli  similar 
to  those  upon  the  bark  soon  develop  in  concentric  circles. 

When  the  cankers  are  few,  on  small  trees,  excision  may 
be  practiced  to  advantage;  when,  however,  there  are  hun- 
dreds of  cankers  upon  each  tree,  this  treatment  is  manifestly 
impracticable.  Spraying  with  strong  Bordeaux  mixture  in  the 
fall,  after  the  crop  is  gathered  and  again  after  an  interval  of 
about  three  weeks,  is  valuable  to  prevent  the  formation  of  new 
cankers,  and  has  established  practical  control  of  the  disease. 

Blister-canker  ^^"^^  (Nummularia  discreta  (Schw.)  Tul).  — 
Attention  in  America  was  first  called  to  this  active,  parasitic 


Pomaceous  Fruits 


45 


disease  in  1902  l)y  Hasselbring,  who  attributed  to  it  more 
serious  results  than  from  any  other  canker  disease  of  IlUnois. 
In  many  cases  largo  lim])s  and  even  whole  trees  are  killed.  It 
has  been  reported  in  many  states,  including  Arkansas,  Okla- 
homa, Nebraska,  New  Hampshire,  New  York,  and  Virginia. 

The  cankers  arc  at  first  in- 
conspicuous, unhealthy,  dirty 
brown,  usually  depressed 
spots  in  the  bark,  sometimes 
15  cm.  in  diameter,  which 
enlarge  rapidly,  particularly 
lengthwise  upon  the  limb,  a 
crack  often  marking  the 
boundary  between  dead  and 
sound  bark.  The  interior  of 
the  bark  of  such  spots  is 
mottled  with  dead  regions. 

In  autumn  the  sporiferous 
bodies  appear  near  the  bor- 
ders of  the  diseased  spots,  first 
pushing  through  cracks  in 
the  bark,  and  exposing  pale 
grayish  ochre-colored  fungous 
growths  3-6  mm.  in  diani- 
eter,which,  when  mature,  are 
slightly  saucer-shaped,  and 
dark  in  color.  These  bodies 
are  attached  to  the  dead 
wood,  and  remain  there  even 
after  the  bark  has  fallen 
away,    thus    constituting    a 

diagnostic  character  of  absolute  reliability,  separating  this 
from  all  other  cankers.  Discoloration  of  the  heartwood 
often  occurs  at  a  distance  of  a  meter  or  more  from  the  ap- 
parent seat  of  disease. 

When  the  cankers  become  large,  injury  to  the  distal  parts 
through   interruption   of  the   water   supply   results.     The 


Fig, 


19.  —  Black-spot  on  fruit. 
After  Lawrence. 


46 


Diseases  of  Economic  Plants 


leaves  show  symptoms  of  disease,  and  the  fruit  fails  to  grow 
to  full  size.    With  complete  girdling  the  limb  dies. 

Since  all  infection  seems  to  occur  through  wounds,  pre- 
vention must  look  largely  toward  the  avoidance  of  wounds 


Fig. 


20.  —  Blister-canker.     Some  of  the  discs  have  been  re- 
moved to  show  the  underlying  marking. 


by  tools,  machinery,  harnesses,  pickers'  ladders,  boots,  etc. 
It  is  also  an  excellent  sanitary  measure  to  cut  out  and  burn 
all  infective  material,  and  in  incipient  cases  excision  of 
diseased  tissue  in  a  limb  may  be  practiced  with  profit. 


Pomaceous  Fruits 


47 


'^Leaf-spots  ^^"^'^  (various  fungi)  (see  also  black-rot,  p.  42). 
—  Aside  from  the  leaf  diseases  of  apple  already  mentioned, 
there  are  numerous  other  leaf-spots  due  to  various  causes. 
These  spots  partake  of  the  same  general  character.  That  is, 
they  are  brown  to  tan-col- 
ored, at  first  circular,  later 
irregularly  circular,  defi- 
nitely bordered,  and  usually 
concentrically  marked.  If 
abundant,  or  if  they  enlarge 
rapidly  upon  the  leaves, 
they  cause  their  premature 
fall,  and  largely  defoliate 
the  tree.  Such  spots  pre- 
vail to  greater  or  less  ex- 
tent in  all  apple  orchards 
but  are  most  destructive 
in  the  Southern  states. 
Numerous  species  of  fungi 
have  been  isolated  from 
these  spots;  some  of  them 
undoubtedly  sustain  a 
causal  relation  to  the  dis- 
ease. Sheldon  claims  that 
in  West  Virginia  much  of 
the  apple  leaf-spot  is  due 
to  an  Illosporium. 

Whatever  the  actual 
causal  fungi  may  be,  these 
spots  are  all,  or  nearly  all, 
of  fungous  origin  and  are 
amenable  to  preventive 
spraying.  The  first  of  three  or  four  applications  should  be 
given  with  the  opening  of  the  leaf  buds. 

Hypochnose  "^'  ^''  {Corticium  stevensii  (Noack)  Burt).  — 
Superficially  this  disease  resembles  the  blight,  with  which  it 
is  hkely  to  be  confounded  by  the  casual  observer.     It  may 


Fig.  21,  —  Apple  leaf-spot  in  late 
stage  of  development,  showing 
concentric  rings.    Original. 


48 


Diseases  of  Economic  Plants 


readily  be  distinguished,  however,  by  two  characters:  first, 
the  manner  in  which  the  leaves  droop  and  mat  together, 

which  is  quite  different 
from  the  habit  of  the 
blight,  the  leaves  of 
which  neither  droop  nor 
become  matted;  second, 
Ijy  the  presence  of  small 
sclerotia,  white  when 
young,  cinnamon-brown 
when  mature,  upon  the 
twigs  adjacent  to  the 
affected  leaves.  These 
sclerotia  usually  meas- 
ure about  2-3  mm. 
in  diameter.  Together 
with  the  sclerotia  and 

J'slk  '  \       d  ^  '^''  extending      along     the 

il^l^^HftpJmv  ••  ^'^^^  longitudinally  are 

^mx  Imm^mJm^S  '  q^^q  found  silvery,  glis- 

tening, thread-like,  fun- 
gous growths. 

This  fungus  hiber- 
nates in  the  sclerotia 
on  or  near  the  terminal 
Inid  and  thence  invades 
the  new  twigs  as  they 
develop,  reaching  out 
upon  each  leaf,  spread- 
ing over  its  under  sur- 
face in  almost  invisible 
thinness,  and  causing  it 
to  droop,  die,  and  eventually  to  fall  away.  Thus,  in  early 
autumn,  such  trees  are  nearly  or  quite  defoliated.  The 
fruit  may  also  be  invaded  by  the  fungus. 

Hypochnose,  first  described  from  Brazil,  is  known  from 
Maine  to  Florida  and  Texas.    It  seems  to  be  especially  de- 


FlG. 


22.  —  Hypochnose,   showing  mat- 
ting of  leaves.    Original. 


Pomaceous  Fruits 


49 


structive  in  regions  of  exces- 
sive humidity,  particularly 
in  the  deep  mountain  valleys 
of  the  Appalachians,  where 
whole  orchards  are  some- 
times seriously  affected. 

Owing  to  the  entirely  su- 
perficial nature  of  the  fungus 
which  causes  the  disease, 
and  its  habit  of  hibernating 
upon  the  twigs,  the  trees 
should  be  sprayed  with  a 
strong  cleansing  mixture, 
Bordeaux  or  bluestone,  be- 
fore the  buds  open,  and 
again  just  before  the  blos- 
soms open. 

Pink-rot  ^^  {Cephalothe- 
cium  roseum  Cda.).  —  This 
rot  is  known  in  many  states. 
It  follows  apple  or  quince 
scab  and  may  be  recognized 
by  the  white,  mildew-like 
growth  which  appears  in 
conjunction  with  the  scab 
which  it  soon  after  entirely 
overgrows  and  turns  to  a 
pink  color. 

While  the  decay  is  really 
caused  by  Cephalothecium, 
a  rupture  made  in  the  skin 
by  the  scab  fungus  is  the 
usual  place  of  entrance.  The 
decayed  spot  is  shallow  and 
slow-growing  as  compared 
with  other  rots.  It  is  ac- 
companied by  a  bitter  taste 


Fig.  23.  —  H3^ochnose,  showing 
sclerotia  on  twig  at  left  and  rhi- 
zomorphic  strands  on  twig  at 
right.    Original. 


50 


Diseases  of  Economic  Plants 


which  is  so  pronounced  as  to  injure  cider  made  from  affected 
apples.  The  chief  destruction  follows  the  harvest,  though 
the  disease  is  sometimes  found  in  fruit  still  upon  the  tree. 

The  Rhode  Island  Greening,  Fall  Pippin,  Fameuse, 
Maiden  Blush,  Tompkins  King,  and  Twenty  Ounce  are 
especially  susceptible. 

Chief  attention  should  be  directed  to  the  prevention  of 


Fig.  24.  —  Pink-rot  following  scab.    After 
Anderson. 

scab.  In  storage  a  dry  house,  well  ventilated,  kept  at  0°  C. 
(32°  F.)  gives  best  rot  resistance. 

Another  form  of  pink-rot  due  to  a  species  of  Hypochnus 
has  been  described  by  Eustace  ^^  especially  upon  Baldwins 
and  Rhode  Island  Greenings.  There  is  no  large  surface 
growth  of  the  fungus  on  the  diseased  spot,  but  the  rot  often 
extends  to  the  core. 

Powdery-mildew  ^^'  ^-  {Podosphceral  eucoiricha  (E.  &  E.) 
Salm.,  Oidium). — The  general  appearance  of  this  mildew 
is  similar  to  grape  mildew;  that  is,  the  surfaces  of  the  leaves 


Pomaceous  Fruits  51 

are  more  or  less  covered  with  a  white  or  grayisli  fungous 
growth,  in  the  later  stages  of  which  are  found  numerous  very 
small  black  fruiting  bodies  approximately  0.25  mm.  in 
diameter.  This  fungus,  while  of  comparatively  little  sig- 
nificance to  old  apple  trees,  causes  much  injury  to  nursery 
stock,  often  becoming  so  serious  as  to  prevent  successful 
budding.  Mildew  has  been  reported  as  especially  serious  in 
California  and  other  states  west  of  the  Rocky  Mountains, 
and  is  of  some  importance  in  all  apple  regions.  In  the  Pajaro 
Valley  the  fungous  mycelium  has  been  shown  to  hibernate 
in  the  buds,  resulting  in  early  spring  infection  of  shoots. 

Another  species  of  mildew,  P.  oxyacanthce  (DC.)  De  Bary, 
shows  the  same  general  characters  as  the  mildew  described 
above,  but  is  of  less  economic  importance.  Three  or  four 
lime-sulfur  sprayings  at  intervals  of  about  two  weeks, 
beginning  when  the  buds  commence  to  open,  have  given  best 
results. 

Crown-gall.     See  peach. 

Soft-rot,  blue-mold  rot  {Penidllium  expansum  Lk.).  —  Per- 
haps the  most  common  apple  rot  is  found  upon  stored  apples 
late  in  the  year.  The  light,  tan-colored  rotted  area  is  soft 
and  watery.  The  decay  results  in  the  complete  loss  of  the 
affected  fruit,  and,  by  contagion,  in  loss  to  the  fruit  mass. 

Upon  cracks  in  the  decayed  surface,  and  eventually  over 
the  whole  rotten  part,  appear  tufts  of  very  short  delicate 
fungous  threads,  at  first  white,  soon  bluish-green,  very  like 
the  common  blue-mold  so  familiar  to  the  housewife  upon 
canned  fruit,  the  seal  of  which  has  permitted  air. to  enter. 
This  blue  substance  upon  the  rotten  apple  consists  of  myriads 
of  the  spores  of  the  causal  fungus.  This  fungus  is  compara- 
tively unaggressive  and  cannot  force  its  way  into  perfectly 
healthy  tissue;  a  bruise  or  rupture  of  the  skin  is  necessary 
to  its  invasion.    The  best  preventive  is  care  to  avoid  bruising. 

Root-rot^''  (various  fungi).  —  Death^  of  trees,  without 
apparent  reason  from  evidence  above  ground,  is  frequently 
due  to  disease  and  decay  of  the  roots.  While  the  earlier 
symptoms  may  vary,  in  general  they  include  an  abnormally 


52 


Diseases  of  Economic  Plants 


large  set  of  small  fruits,  and  in  the  following  season  few 
flowers,  deficient  growth,  and  small  leaf  development  and 
perhaps  chlorosis.  In  cases  where  only  a  few  roots  are 
diseased  the  evident  effects  may  be  limited  to  the  correspond- 


FiG.  25.  —  Clitocybe  upon  apple.    After  Wilcox. 

ing  side  of  the  tree.  Several  years  may  elapse  between  the  ap- 
pearance of  the  first  symptoms  and  final  death.  The  roots, 
one  or  all,  of  trees  well  advanced  in  disease  show  decay,  de- 
pendent in  character  upon  the  causal  fungus.  Several  dif- 
ferent fungi  cause  root-rot  (see  p.  370).  Among  those  most 
common   on   fruit   trees   are:    Clitocyhe   parasitica   Wil.      A 


Pomaceous  Fruits  53 

gummy  exudate  is  usually  present  around  the  base  of  the  tree 
and  black  rhizomorphs  adhere  to  the  roots.  In  late  stages 
clusters  of  the  gill-bearing  sporophores  (Fig.  25)  develop; 
Armillaria  mellea  Vahl.  Quantities  of  black,  stringy,  hard, 
shiny  strands  1  to  2  mm.  in  diameter  occur  around  the  roots 
and  in  the  adjacent  soil.  The  gilled  sporophores  appear  later 
(p.  370);  Fomes  annosus  (Fr.)  Cke.  The  sporophores  are 
pore-bearing  (p.  371); 
Septobasidium  sps.  with 
smooth  pore-bearing 
surfaces;  Ozonimn  om~ 
nivorum,  Sh.  See  Texas 
root-rot  (p.  23);  Xyl- 
aria  sps.^^  The  affected 
roots  are  covered  with 
a  thin,  compact  growth 
of  mycelium,  white  at 
first,  later  developing 
into  a  black  incrusta- 
tion. Minute,  thread- 
like rhizomorphs  ra-  ^^V^^- -Br«wn-rot  produced  by  inocu- 
'^        .  lation.     JNote  the  lungus  lorms  the  let- 

diate   several   centmie-      ters  A.  M.  C.    Original, 
ters    along    the     root. 
Affected  roots  are  soon  girdled   and  the  distal  parts  die. 

Root-rot,  due  to  one  or  another  of  these  causes,  is  of  wide 
and  common  occurrence,  and  results  in  large  loss.  It  is 
found  more  frequently  on  newly  cleared  land  than  elsewhere. 
When  the  disease  has  advanced  far  enough  to  be  recognized, 
no  cure  is  available,  and  it  is  unsafe  to  replant  in  the  infested 
place.  Wood  bearing  root-rot  fungi  should  be  burned  to 
lessen  infection. 

Wood-rot  '^''  of  orchard  trees  is  of  the  general  character  dis- 
cussed under  Decay  in  live  trees  on  page  354.  It  is  a  very 
important  source  of  loss  on  fruit  trees  of  all  kinds,  about 
one-half  of  all  bearing  trees  being  infected.  The  rot  may 
chiefly  be  avoided  by  preventing  wounds  or  by  treating  them 
with  disinfectants.    See  p.  378. 


54  Diseases  of  Economic  Plants 

Frost  Injury.  ^^  —  Varieties  of  apples  differ  from  each  other 
ill  their  susceptibihty  to  injury  from  cold.  The  injury  may 
be  local,  on  single  twigs,  or  spots  on  twigs,  body,  or  branch; 
or  general,  affecting  the  whole  tree.  The  damage  may  be 
apparent  externally  or  show  at  first  only  in  a  discolored 
cambium.  ''  Sun  scald,"  in  which  the  frosted  bark  occurs  as  a 
cankered  area  and  either  i:)eels  off,  or  clings  tightly  and  is 
sunken,  is  a  frost  injury.  Twigs  may  l;e  killed  outright, 
especially  if  the  wood  has  not  ripened  properly.  Late  spring 
frosts  injure,  as  is  well  known,  the  buds,  blossoms,  etc. 
Frost  cankers  may  form  the  threshold  for  the  entrance  of 
various  fungi  and  thus  pave  the  way  to  disease,  e.  g.  black- 
rot  or  bitter-rot  cankers.  A  cover  crop  tends  to  lessen  frost 
injury,  by  diminishing  excess  moisture  in  the  fall,  while 
avoidance  of  cultivation  late  in  the  season  hastens  maturing 
of  the  wood. 

Bitter-Pit  ^^  consists  of  a  pitting  of  the  fruits  with  slightly 
sunken  circular  spots  varying  from  mere  dots  to  5  mm.  in 
diameter,  which  finally  become  brown.  The  tissue  at  the 
bottom  of  the  pit  is  dead,  brown,  and  spongy.  Similar  lesions 
may  occur  deep  within  the  tissue  of  the  ajaple.  No  parasite 
is  present  and  the  trouble  seems  to  be  due  to  improper  water 
relations.  The  disease  causes  considerable  loss  over  a  large 
range  of  territory.  Thinning  the  fruit  to  a  proper  set  lessens 
the  damage.  Pitted  fruit  should  either  be  consumed  at 
once  or  stored  or  shipped  under  low-temperature  conditions 
(30°-32°  F.,— 1°-0°  C.) 

Jonathan-Spot '''•''  "^  occurs  on  several  varieties  of  apples 
including  the  Jonathan,  Esopus,  Wealthy,  Ortley,  and  Wolf 
River.  The  spots  are  circular,  2-15  mm.  in  diameter, 
abruptly  but  slightly  depressed,  light  brown  in  color,  and 
are  more  superficial  than  those  of  bitter-pit.  The  disease 
may  appear  on  fruit  still  on  the  tree  or  may  develop  during 
storage  or  transit.  The  cause  is  unknown.  Fruits  of  variety 
tending  to  spot  should  be  consumed  early  or  placed  in  cold 
storage. 

Scald  '''^  is  a  storage  trouble  particularly  serious  on  im- 


Pomaceous  Fruits  55 

mature  apples.  It  is  duo  to  gases  given  off  from  apples  and 
ma}"  be  avoided  l)y  aeration. 

Minor  diseases. 

European  canker  ■'-  {Nedrin  galligena  Bros.).  —  The  Euro- 
pean canker  was  not  recorded  upon  the  apple  in  America 
prior  to  1899,  when  Paddock  mentioned  its  presence  in  Nova 
Scotia  and  New  York.  Later  it  was  noted  in  New  Hampshire 
and  Ohio  and  is  now  known  to  be  widely  distril)uted  from 
the  Atlantic  to  the  Pacific.  It  constitutes  a  serious  disease 
in  Europe  and  may  become  of  importance  here.  The  canker 
enlarges  year  after  5^ear,  but  more  slowly  than  black-rot 
canker,  and  displays,  when  fruiting,  numerous  minute,  deep 
red  perithecia  which  serve  to  distinguish  it  from  other 
cankers. 

Brown-rot  ^°  {Sclerotinia  ciiierea,  Monilia).  —  One  of  the 
most  serious  apple  rots  in  Europe,  this  disease  fortunately  is 
not  as  yet  destructive  in  America,  though  Sclerotinia  cinerea 
is  occasionally  met  with  as  one  of  the  minor  causes  of  apple 
losses.  It  has  been  observed  in  several  states,  notably  New 
York,  Missouri,  Nebraska,  the  Virginias,  North  Carolina, 
Illinois,  Minnesota,  Arkansas,  and  New  Mexico  frequently 
enough  to  call  for  printed  mention.  Brown-rot  produces 
complete  decay  of  the  affected  apples,  which  turn  brown,  or 
later  black,  become  soft  and  wrinkled,  and  soon  show  pustules 
of  bushy  mycelium  breaking  through  rifts  and  fissures  in  the 
skin  over  the  diseased  tissue.  The  diseased  fruits  may 
mummify  upon  the  tree  or  more  frequently  fall  to  the  ground 
and  there  shrivel  to  dry,  hard,  wrinkled  masses,  in  which  the 
rot  fungus  winters. 

.Sooty-blotch'*^-  {Glcendes  pomigena  (Schw.)  Colby). — 
Irregular,  soot}",  black  blotches,  especially  conspicuous  on 
the  lighter  colored  varieties  of  apples,  are  frequently  seen 
upon  unsprayed  fruit.  The  individual  blotches  measure 
from  0.5-2  cm.  across  and  are  often  so  abundant  that  they 
coalesce,  giving  the  fruit  a  dirty  appearance.  The  fungus 
attacks  the  fruit  late  in  the  season,  and  is  strictly  superficial. 


56  Diseases  of  Economic  Plants 

It  may  easily  be  rubbed  off  with  a  cloth.  The  loss  in  ready 
salability,  due  to  the  unsightliness  of  the  fruit,  is  reason 
enough  for  protective  sprayings.  Bordeaux  mixture  applied 
at  intervals  of  about  two  weeks  from  the  middle  of  June  until 
the  middle  of  August  is  effective. 

-Fly-speck.  ^"-  —  Growing  upon  the  surface  of  the  fruit  and 
forming  numerous  clustered  black  specks  closely  resembling 


Fig.  27.  —  Fly- speck  (at  left);  Sooty-blotch  (at  right).    After  Colby. 

fly-specks,  this  fungus  causes  disfigurement  of  the  apple. 
The  generic  position  of  the  fungus  is  in  doubt,  though  it 
was  originally  named  Lahrella  pomi  by  Montague. 

Volutella  rot*^^  (Volutella  fructi  S.  &  H.).  —  In  general 
appearance  the  volutella  rot  is  not  readily  distinguished  from 
black-rot,  though  the  texture  of  the  rotted  tissue  is  much 
firmer  and  drier.  Under  the  hand  lens  the  sporiferous 
pustules  are  seen  to  be  clothed  with  numerous  hairs,  which 
character  sufficiently  marks  it  as  a  separate  disease.  It  has 
been  reported  from  North  Carolina,  New  York,  Wisconsin, 
and  is  probably  of  general  distribution. 

Scurf,  an  affection  of  the  bark  of  twigs,  is  due  to  Phyllo- 
stida  prunicola  (Opiz.)  Sacc. ;  Bark-canker  '-  due  to  Myxospo- 


Pomaceous  Fruits  57 

riu7n  corticolum  Edg.  is  superficial  on  Ijoth  apples  and  pears 
and  of  little  importance;  the  Fmit-spot/^' ''^  {Phonia  pomi 
Pass.),  occurs  in  the  northeastern  United  States,  the  spots 
are  small,  sunken,  brown  or  black;  Rough-bark"'-  is  caused 
by  Phomopsis  mali  Rob.  The  Septobasidium  canker  is 
due  to  Septobasidium  pedicillatum  (Schw.)  Pat.  Phytophthora 
cadorum  (L.  &  C.)  Schr.  causes  a  fruit  rot.  Black-mold, 
due  to  Fumago  vagans,  is  superficial,  while  black-mold  due 
to  Alternaria  sps.  produces  a  core  rot.  Plenodomus  can- 
ker ^'°  (Plenodomus  fusco-maculans  (Sacc.)  Coons)  kills  the 
cortex,  which  eventually  flakes  off  in  long  strips  leaving 
the  wood  bare.  Die-back  canker  ^^^  (see  peach)  is  occa- 
sionally present,  also  Fruit  rots  due  to  Endomyces  and 
Rhizopus.  Rosette,  which  resembles  peach  rosette,  has 
been  noted  in  three  states. 


Conditions  Infi,uencing  the  Spraying  Schedule  for 
Apple  Disease  * 

A  spraying  schedule  which  may  give  the  best  result  in  one 
part  of  the  country  when  used  in  spraying  a  certain  variety 
may  be  unsatisfactory  in  another  part  of  the  country,  or 
for  another  variety  or  in  another  season,  or  in  another 
orchard  in  the  same  part  of  the  country.  No  attempt  is 
made,  therefore,  to  present  definite  spraying  schedules,  al- 
though an  attempt  is  made  to  present  briefly  the  considera- 
tions which  govern  them. 

Primarily,  sprays  are  applied  commercially  to  control 
apple  scab,  apple  blotch,  and  bitter-rot.  The  control  of  other 
fungi  with  the  exception  of  apple  rust  is  usually  incidental  to 
the  control  of  these  three. 

To  secure  the  best  results  it  is  necessary  to  make  the  first 
application  of  fungicide  before  the  first  infections  take  place, 
and  to  repeat  at  sufficient  intervals  to  give  protection  from 
this  time  on.    In  general,  it  may  be  said  that  the  first  apple- 

*  Prepared  by  W.  A.  Ruth. 


58 


Diseases  of  Economic  Plants 


scab  infections  usually  occur  about  the  time  the  trees  are 
blossoming,  and  that  serious  damage  may  be  caused  by  in- 
fections taking  place  for  four  or  five  weeks  after  the  petals 
have  fallen;  that  the  first  serious  infections  of  apple  blotch 
may  take  place  three  or  four  weeks  after  the  petals  have 
fallen,  and  that  further  infections,  resulting  in  serious  damage, 
may  occur  for  a  period  of  five  or  six  weeks;  that  the  first 
infections  of  ])itter-rot  may  occur  about  the  middle  of  June, 


Fig.  28.  —  Unsprayed  apple  trees.    After  Scott  and  Rorer. 


the  period  of  possible  infection  continuing  throughout  the 
season,  the  probability  of  infection  being  greatest  in  hot,  wet 
weather. 

The  choice  of  the  fungicide  and  the  decision  as  to  when  to 
spray  are  governed  by  several  considerations.  These  include 
the  local  conditions,  among  which  may  be  placed  varietal 
susceptibility  to  apple  scab,  and  the  probable  local  varietal 
susceptibility  to  other  fungi,  seasonal  weather  conditions, 
and  varietal  susceptibility  to  spray  injury. 

Locality.  —  Apple  scab,  apple  blotch,  and  bitter-rot  are  so 


Pomaceous  Fruits 


59 


distributed,  as  to  the  localities  in  which  they  produce  serious 
injury,  that  in  the  northern  apple-growing  regions  of  the 
eastern  United  States  orchardists  spray  chiefly  to  control 
apple  scab;  in  southern  apple-growing  regions,  it  may  be 
necessary  to  control  apple  scab,  apple  blotch,  and  ])itter-rot; 
and  in  other  regions  to  control  scab  and  blotch.  The  general 
climatic  relationship  of  these  fungi  in  the  eastern  United 
States   may   be   illustrated    roughly   by   their   behavior   in 


Fig.  29. 


Sprayed  apple  trees  from  the  same  orchard  as  tho.se 
shown  in  Fig.  28. 


Illinois.  Apple  scab  is  a  serious  disease  in  all  parts  of  the 
state;  apple  blotch  is  a  serious  disease  as  far  as  40°  north 
latitude;  and,  ordinarily,  bitter-rot  does  not  cause  serious 
damage  north  of  39°  latitude.  It  is  thus  necessary,  in  the 
northern  part  of  the  state,  to  spray  for  apple  scab  only; 
toward  the  southern  part,  it  is  necessary  to  spray  for  apple 
scab  and  apple  blotch;  and  still  farther  south,  to  spray  to 
control  apple  scab,  apple  blotch,  and  bitter-rot. 


60  Diseases  of  Economic  Plants 

The  relation  between  the  apple  and  its  parasitic  fungi 
seems  to  vary,  however,  within  more  restricted  areas.  This 
may  be  illustrated  as  follows:  The  practice  in  the  eastern 
United  States  has  been  to  apply  the  first  spray  for  apple 
scab  just  before  the  blossoms  open,  when  the  flowers  in  the 
cluster  have  separated  from  each  other,  and  the  pink  petals 
are  showing.  (This  is  called  the  "pink,"  or  "cluster-bud," 
spray.)  Wallace, ^^  after  studying  the  period  of  ascospore  dis- 
charge, stated,  in  1913,  that  there  seems  to  be  little  danger  in 
New  York  that  infections  of  apple  scab  will  occur  much 
earlier  than  blossoming  time,  and  that  the  cluster-bud  spray 
is  sufficiently  early.  Childs,^"^  as  a  result  of  similar  study, 
later  showed  that,  in  Oregon,  two  applications  must  be  made 
before  the  bloom,  the  first  coming  when  the  leaves  are  quite 
small,  followed  by  the  "cluster-bud"  spray.  Since  then 
various  spraying  schedules  have  been  worked  out  experi- 
mentally in  the  East.  Thus,  Blair  ''^'^  in  Nova  Scotia,  recom- 
mends two  applications  before  the  bloom,  while  Morse's 
work  ^^^  in  Maine  may  be  taken  to  show  that  in  the  locality 
from  which  his  data  were  drawn  little  or  no  infection  occurs 
before  the  blossoming  period. 

The  relation  differs  not  only  with  the  locality  but  also  with 
the  variety  of  apple.  Varietal  susceptibility  to  or  immunity 
from  attack  by  one  fungus  is  not  necessarily  correlated  with 
the  same  relation  toward  another.  This  relationship  seems 
to  require  local  determination.  The  most  susceptible  va- 
rieties demand,  of  course,  the  most  thorough  treatment. 
The  subject  of  varietal  susceptibility  to  apple  scab  has  been 
summarized  by  Wallace. "^^  (1)  Certain  varieties  may  appear 
to  be  immune  in  one  season  but  may  be  very  susceptible  in 
another  season,  under  different  weather  conditions.  (2)  A 
variety  may  be  resistant  in  one  year  and  susceptible  in  an- 
other year  under  conditions  which  for  average  varieties  are  as 
favorable  to  the  disease  in  the  one  case  as  in  the  other. 

(3)  Varietal  susceptibility  may  differ  in  different  localities. 

(4)  Only  in  rare  cases  is  a  variety  consistently  and  relatively 
immune  over  as  short  a  period  as  five  years.    The  apparent 


Pomaceous  Fruits  61 

immunity  may  increase  or  decrease.  (5)  No  variety  is  abso- 
lutely immune. 

Varietal  susceptibility  to  scab  differs  so  markedly  in 
different  localities  that  general  lists  are  of  little  value.  The 
Ben  Davis,  for  example,  which  is  generally  considered  rela- 
tively immune  to  scab,  is  very  susceptible  in  Illinois.  The 
Yellow  Transparent,  stated  to  be  seriously  injured  by  scab 
in  Ohio,  ''^^  is  relatively  immune  in  southern  Illinois,  and  the 
Grimes,  which,  in  Ohio,  is  moderately  injured  by  scab,  is 
relatively  immune  in  Illinois.  The  Rome  Beauty  is  seriously 
injured  in  both  localities. 

Weather  Conditions.  —  Weather  conditions  play  a  very 
important  role  in  the  outbreak  of  a  disease.  Wallace  ^^ 
states  that  ''The  ideal  condition  for  scab  infection  is  a  gentle, 
continued  rain  followed  by  cloudy,  calm  weather  and  a 
saturated  atmosphere,  in  which  cases  the  spores  are  kept 
wet  for  a  long  time  in  one  position.  Ascospores  have  been 
known  to  germinate  in  a  period  of  four  hours,  but  it  is 
probable  that  in  order  to  produce  abundant  infection 
the  trees  must  be  kept  wet  for  eight  or  ten  hours  or 
even  longer."  Ascospore  discharge  begins  almost  as  soon 
as  rain  begins,  or  within  five  minutes  after  the  time  the 
leaves  are  wet  and,  under  continuously  wet  conditions, 
an  interrupted  discharge  of  spores  can  be  expected  for 
some  time.^^ 

Roberts  ^^  states  that  the  dependence  of  apple-blotch 
infection  upon  rainy  weather  in  orchards  in  the  Ozark  section 
is  very  noticeable,  but  in  Kansas,  where  the  sources  of  infec- 
tion —  that  is,  the  twig  cankers  —  are  much  more  numerous, 
the  dependence  is  less  noticeable. 

"The  conditions  most  favorable  for  the  development  of 
bitter  rot  are  (1)  a  period  of  hot  weather  accompanied  by 
frequent  rains  and  heavy  dews  at  a  period  when  the  apple 
crop  is  approaching  maturity,  i.  e.,  from  the  middle  of  July 
to  the  end  of  August.  (2)  Numerous  sources  of  infection, 
i.  e.  cankers  on  the  limbs  and  mummified  fruits  left  hanging 
on  the  trees."    Blair,^^  from  whom  the  above  is  quoted,  sum- 


62  Diseases  of  Economic  Plants 

marizes   the   results   of   observation   covering   six   y(>ars   in 
Illinois  as  follows: 

"It  may  be  safely  concliKUHl  that  moist  weather  with  a 
considerable  precipitation  and  a  high  temperature  are 
favorable  to  the  spread  and  growth  of  bitter-rot.  There  was 
no  opportunity  to  note  the  effect  of  moist,  cold  weather 
though  it  might  be  argued  from  analogy,  there  being  no 
evidence  of  the  disease  in  northern  and  very  little  in  central 
Illinois,  where  the  rainfall  is  abundant  and  the  mean  tempera- 
ture lower,  that  moisture  without  high  temperature  is  not 
favorable  to  the  development  of  the  disease.  Hot  weather 
alone  unaccompanied  by  moisture  proved  unfavorable  to 
the  spread  of  the  disease,  as  seen  in  the  season  of  1901, 
but  hot  weather  alone  did  not  prevent  the  disease  from 
accomplishing  its  work  of  destruction  after  infection  had 
once  occurred,  as  was  observed  in  1900  when  the  dry  month 
of  August  followed  the  abnormally  wet  months  of  June 
and  July." 

The  spraying  schedule  should  be  adjusted  to  meet  the 
weather  conditions.  Rainy  weather  not  only  provides 
favorable  conditions  for  infection  but  removes  the  protecting 
spray.  ^ 

\ 

PEAR  ■'^'■ 

■  Fire-blight,  blight  '•''~'^'  ^^-^  {Bacillus  amylovorus  (Burr.) 
Trev.)."— The  name  "fire-blight"  is  well  chosen,  since  the 
affected  tree,  with  its  shriveled  branches  and  shrunken, 
blackened  twigs,  gives  the  impression  of  fire  injury.  During 
the  winter  diseased  twigs  may  be  recognized  by  the  dead, 
shriveled  leaves  still  clinging  to  them.  In  the  early  spring, 
these  leaves  still  persist,  while  on  closer  examination  the 
bark  and  wood  of  the  blighted  twigs  are  seen  to  be  black 
and  dead.  This  blight  is  the  most  important  disease  of 
the  pear  and  is  also  serious  on  the  apple,  quince,  and  haw- 
thorn, and  to  some  extent  it  affects  plum,  apricot,  and 
mountain  ash. 


Pomaceous  Fruits 


63 


Fire-blight  was  first  described  in  1794  from  the  Hudson 
Valley,  whence  it  spread  in  every  direction,  reaching  Califor- 
nia about  1900.     In  many  cases  even  whole  orchards  have 


■■——A  ;  -^^tmr.--^      mim^ms-  ^■■^— 

P'iG.  30.  —  Fire-blight;  healthy  and  diseased  twigs. 
Original. 

succumbed  to  its  attack.  One  pear  grower  near  Washing- 
ton, D.  C,  estimated  his  loss  from  this  one  disease  in  one 
year  at  $10,000.  It  is  as  yet  confined  to  North  America  and 
is  more  severe  in  the  Southern  than  in  the  Northern  states. 


64  Diseases  of  Economic  Plants 

So  diverse  and  numerous  were  the  early  theories  as  to  the 
nature  and  cause  of  bUght,  knd  so  fruitless  were  the  discus- 
sions in  earlier  years  that  the  Western  New  York  Horticul- 
tural Society  passed  resolutions  to  prohibit  further  reference 
to  the  subject  until  entirely  new  facts  were  forthcoming. 
Among  the  numerous  theories  may  be  mentioned  those 
depending  upon  electrical  or  atmospherical  influences, 
freezing  of  the  bark,  too  long  culture  of  particular  varieties, 
freezing  of  the  roots,  too  high  culture,  insects,  fungi,  and 
lack  of  nutrition.  One  of  the  most  prominent  of  these  was 
Downing's  "frozen  sap  theory,"  according  to  which  the 
disease  is  due  to  the  freezing  and  thawing  of  the  sap,  resulting 
in  loss  of  vitality  and  development  of  poisons  in  the  tissues. 
It  is  unnecessary  to  discuss  any  of  these  theories  further  than 
to  say  that  none  of  them  explains  the  facts. 

In  1878  Burrill  discovered  bacteria  in  the  diseased  twigs, 
and  by  transferring  to  healthy  twigs  some  of  the  exudate 
from  diseased  tissue  bearing  these  bacteria  was  able  to 
cause  the  disease.  Arthur  later  grew  the  bacteria  in  pure 
cultures  and  with  these  cultures  produced  the  disease.  It 
was  thus  proved  beyond  question  that  bacteria  cause  the 
blight. 

It  has  been  demonstrated  that  the  germs  cannot  gain 
access  through  healthy,  mature  bark,  but  will  readily  pene- 
trate into  wounds,  or  into  floral  parts. 

This  blight  bacillus  deposited  upon  the  flower,  or  upon 
tender  shoots,  gains  entrance  and  rapidly  grows  downward 
through  the  wood  and  bark,  causing  the  foliage  upon  the 
affected  twig  to  die.  The  disease  rarely  progresses  more 
than  5-8  cm.  in  one  day,  though  even  0.3  meter  is  occasionally 
reached.  Ordinarily,  sick  twigs  dry  out,  progress  of  the 
disease  soon  stops,  and  the  germs  in  the  twig  die.  Waite 
found  that  in  some  limbs,  probably  one  of  several  hundred, 
the  disease  remains  active.  Two  forms  of  blight  are  thus 
distinguished :  one  very  dangerous,  the  other  no  longer  offen- 
sive. It  is  the  limbs  still  in  condition  of  ''active  blight"  that 
carry  the  pest  over  winter. 


Pomaceous  Fruits 


65 


With  the  flow  of  sap  in  the  spring  these  infested  hmbs 
exude  a  milky  fluid  teeming  with  the  bacteria  and  thus  be- 
come centers  of  reproduction.  It  has  been  demonstrated  that 
several  species  of  insects  can  carrj^  infection,  but  it  is  not 
probable  that  they  are  really  important  agents  of  transmis- 
sion."^ Two  additional  forms  of  this  disease,  according  to  the 
part  affected,  are  recognized:  (1)  blossom-blight,  (2)  body- 
bhght  and  canker. 

Neither  of  these  differs  essentially  from  twig-blight, 
though  body-blight  or  canker  is  especially  worthy  of  men- 
tion on  account  of  its  pecul- 
iar destructiveness.  This 
form  occurs  where  infection 
is  led  by  a  spur,  shoot,  or 
sucker,  or  where  the  germ 
enters  through  a  wound 
into  the  body  or  main  hmbs 
of  the  tree.  The  result  is  a 
canker  more  or  less  cir- 
cular, which  may  even 
girdle  the  tree  or  branch, 
and  which  in  any  event 
causes  serious  injury. 

The  susceptibility  of  the  tree  is  largely  influenced  by  ex- 
ternal conditions.  In  general,  anything  that  leads  to  rapid 
growth,  resulting  in  tender  shoots,  favors  the  development  of 
the  disease.  There  is  also  much  difference  in  resistance 
offered  by  different  varieties.  The  Anjou,  Kieffer,  An- 
gouleme,  and  Seckel  possess  more  resistance  than  the  Bartlett, 
Clapp,  or  Flemish  Beauty. 

Based  on  the  facts  as  stated  above,  the  following  sugges- 
tions for  avoiding  the  blight  were  deduced,  and  tested  by 
Waite. 

1.  Pruning  in  winter  when  the  tree  is  dormant  promotes 
growth  and  favors  blight.  Withholding  the  pruning  knife, 
which  may  not  otherwise  be  best  for  the  tree,  will  reduce 
this  tendency. 


Fig.  31.  —  Fire-blight  showing  exu- 
date from  bark,  much  enlarged. 
This  teems  with  the  causal  bac- 
teria.   After  Whetzel. 


66  Diseases  of  Economic  Plants 

2.  Overstimulation  with  fertilizers,  especially  those  rich 
in  nitrogen,  is  to  l)e  avoided. 

3.  A  well-cultivated  tree  is  more  inclined  to  blight  than 
one  growing  on  sod  or  untilled  land. 

4.  In  irrigated  orchards  a  reduction  of  the  water  supply 
to  the  minimum  has  been  found  effective. 

In  nurseries  or  small  orchards  or  in  regions  where  the 
blight  is  not  excessive,  the  disease  may  be  reduced  by  cutting 
out  and  burning  every  particle  of  blight  when  the  trees  are 
dormant.  Not  a  single  case  of  blight  should  be  allowed  to 
survive  the  winter,  either  in  the  orchard  or  within  half  a 
mile  of  it.  Every  pomaceous  tree  near  by,  including  the 
apple,  pear,  quince,  Siberian  crab  apple,  wild  cral:)  apple, 
the  mountain  ash,  service  berry,  and  all  the  species  of  Cratse- 
gus,  or  hawthorns,  should  be  examined  for  this  purpose,  the 
blight  being  the  same  in  all.  The  orchardist  should  not  stop 
short  of  absolute  extermination  in  every  case,  for  a  few  trees 
or  branches  overlooked  may  go  a  long  way  toward  undoing 
all  of  his  work.  Cutting  out  the  blight  may  be  done  at  an}^ 
time  in  the  winter  or  spring  up  to  the  period  when  growth 
begins.  The  best  time,  however,  is  undoubtedly  in  the 
fall,  when  the  foliage  is  still  on  the  trees  and  the  contrast 
between  the  blighted  and  the  healthy  limbs  is  strong.  It 
is  further  necessary  to  make  a  weekly  inspection  of  every 
tree  throughout  the  growing  season,  beginning  when  the 
blossoms  fall,  in  order  to  cut  out  blight  whenever  it  is 
found. 

In  each  case  it  is  essential  to  cut  well  below  any  external 
evidences  of  the  disease.  To  avoid  spreading  the  infec- 
tion, in  case  the  pruning  tools  should  accidentally  cut  into 
the  diseased  tissue,  the  cutting  blade  should  each  time  be 
disinfected  by  wiping  it  with  a  cloth  saturated  with  a  strong 
solution  of  corrosive  sublimate  (1  part  to  1000).  When  the 
wound  made  l)y  this  excision  is  at  all  large,  it  also  should  be 
disinfected  with  the  corrosive-sublimate  solution.  Particular 
care  should  be  taken  to  remove  and  burn  all  diseased  spurs 
and  water  sprouts. 


Pomaceous  Fruits  67 

Unless  continued,  careful  inspection  is  given,  and  concerted 
action  in  a  community  maintained,  but  little  l^enefit  will 
follow. 

Rusf*^' '*-•  ^^'^  {Gymnosyorangium  sps.,  Roestelia).  —  Rust 
of  pear  is  very  similar  in  nature  to  rust  of  the  apple,  though 
less  often  injurious.  It  consists  of  a  summer  stage  and  a 
winter  stage.  The  former  produces  rust  on  the  leaves  of  the 
pear,  while  the  winter  stage  of  the  eastern  form  of  rust  pro- 


FiG.  32.  —  Scab  on  California  pears  bought  in  Raleigh,  N.  C. 
Original. 

duces  the  familiar  cedar-apple  upon  the  cedar  tree.  The  pear 
rust  of  the  West  is  a  distinct  species,  with  the  incense  cedar 
as  the  alternate  host. 

The  remedy,  as  in  the  case  of  the  apple,  consists  in  re- 
moving all  red  cedar  trees  from  the  neighborhood  of  the 
pear  orchard;  thus  eliminating  the  source  of  infection. 
When  this  is  impossible,  the  pear  trees  should  be  sprayed 
with  Bordeaux  mixture  immediately  after  the  early  rains 
which  cause  the  gelatinous  horns  to  emerge  on  the  cedar- 
apple,  and  thus  furnish  the  suppl.y  of  spores  for  the  spring 
infection.  This  disease  of  pears  is  particularly  abundant 
upon  varieties  of  the  Japanese  strain. 

Powdery-mildews.     See  apple. 


68 


Diseases  of  Economic  Plants 


Scab  ^^' "^^  {Venturia  pyrina  Aderh.,  Fusidadium) .  —  This 
scab  much  resembles  that  of  the  apple  and  is  often  accom- 
panied by  a  peculiar  cracked  appearance  of  the  skin.  This 
symptom,  however,  is  secondary  and  is  not  necessarily 
present.    Rough  cankers  are  formed  upon  the  twigs.    Pear 

scab  is  generally  distributed 
throughout  the  United  States 
and  Europe. 

The  use  of  a  dormant 
spray  followed  by  two  appli- 
cations of  Bordeaux  mixture, 
while  the  buds  are  unfolding, 
is  recommended. 

Leaf-spot  ^^  {Mycosphce- 
rella  sentina  (Fr.)  Schr.,  Sep- 
toria).  —  Leaf -spot,  while 
rarely  completely  destructive 
to  foliage  or  crop,  does  inter- 
fere with  the  general  pro- 
ductiveness and  health  of  the 
tree  by  diminishing  its  green 
surface,  often  causing  defoli- 
ation. It  is  known  over  a 
wide  range  and  is  common, 
especially  in  the  Eastern 
United  States  and  in  Europe. 
Leaf-spot  may  be  distin- 
guished from  scab  and  blight 
by  the  fact  that  the  diseased  area  is  rather  sharply  defined 
and  characteristically  angular  in  outline.  The  center  of  the 
spot,  usually  ashen  in  color,  is  surrounded  by  a  narrow  brown 
zone,  and  this  in  turn  by  one  of  purplish  hue.  The  ashen 
center  bears  several  minute,  dark-colored  pycnidia. 

The  treatment  recommended  for  pear  scab  is  preventive. 

Leaf -blight'^    (Fabroea   maculata    (Lev.)   Atk.,   Entomos- 

porium). — This  leaf -blight,  more  serious  than  leaf -spot,  is 

almost   as  widely  distributed  as  is  the  pear  itself,  though 


Fig.  33.  —  Pear  leaf-spot. 
Anderson. 


After 


Pomaceous  Fruits  69 

less  prevalent  in  the  South  antl  West  than  in  the  North 
and  East. 

The  entire  leaf  area  often  presents  a  diseased  appearance, 
and  there  is  no  striking  zonal  arrangement  in  the  infected 
spots  as  in  leaf-spot.  Eventually  the  leaf  yellows,  or  turns 
brown  and  falls.  The  l)light  may  attack  the  fruit  itself,  caus- 
ing a  red  spot,  which  in  a  later  stage  resembles  pear  scab. 

The  treatment  already  recommended  for  pear  seal)  will 
suffice  for  pear  leaf-blight. 

Black-rot  canker  {Physalospora  cydonice,  Sphceropsis.). — ■ 
In  appearance  and  treatment  this  disease  is  similar  to  black- 
rot  of  the  apple. 

Minor  diseases 

Pink-rot  often  follows  seal).  The  cause  and  general  rela- 
tions are  given  under  apple;  Bark-canker,  Frost  injury, 
Crown-gall,  Sooty-blotch,  Fly-speck,  Black-mold,  Brown- 
rot,  Texas  root-rot,  Hypochnose,  Septobasidium  canker, 
Die-back  canker,  Alternaria,  see  apple.  Bitter-rot  is 
identical  with  that  of  the  apple  but  is  of  slight  importance 
on  the  pear.  Red-leaf,  a  disease  of  unknown  cause,  has  been 
noted  in  New  York. 

QUINCE.so 

Rust  '^^'  ■'"'  '"•"'  (Gymn.osporangium  clavipes  C.  &  P.,  Roes- 
telia).  —  The  quince  rust,  spring  stage,  agrees  with  apple 
rust  in  general  characters.  The  causal  fungus  grows  upon 
the  fruit  in  the  summer  and  produces  there  myriads  of  spores 
which,  on  the  approach  of  fall,  are  carried  by  the  wind  to  ad- 
jacent red  cedar  trees  (Juniperus),  and  there  produce  swellings 
upon  the  branches  and  twigs  during  the  fall  and  winter.  In 
the  spring,  these  give  origin  to  masses  of  spores  embedded  in  a 
matrix  of  jelly.  These  spores  are  conveyed  to  the  quince  tree 
by  the  wind,  and  there  again  produce  the  quince  rust.  The 
cedar  is  a  necessary  resting  place  for  this  fungus  during 
the  winter. 


70 


Diseases  of  Economic  Plants 


The  remedy,  therefore,  if  practicable,  is  to  remove  the 
cedar  trees  from  the  neighborhood  of  quince  trees.  This  will 
almost  entirely  pi-event  the  rust,  although  in  rare  instances 
a  few  spores  may  l)e  carried  a  considerable  distance.  In 
case  the  cedar  is  too  abundant  to  permit  of  its  complete 
removal,  resort  must  be  had  to  spraying  the  leaves  and 
fruit   of  the  quince  trees  with  Bordeaux  mixture  at   the 


Fig.  34.  —  Young  quinces  showing  rust.    After  Bailey. 

time  when  the  rust  spores  are  expected  to  arrive;  that  is, 
at  the  time  when  the  gelatinous  spore  masses  are  present  on 
the  cedar-apple. 

Blight  (Bacillus  amylovorus) .  —  This  disease  has  been 
sufficiently  discussed  in  connection  with  the  pear  and  apple. 
It  is  only  necessary  here  to  indicate  that  it  is  the  most  serious 
known  disease  of  the  quince.  The  treatment  is  the  same 
as  that  recommended  for  this  disease  on  other  pomaceous 
trees. 

Leaf -blight,  black-spot  ^"^  (Fabroea  maculata  (Lev.)  Atk., 
Entoinosporiuni). — Both  the  fruit  and  foliage  are  affected 


Pomaceous  Fruits 


71 


by  this  blight,  the  foUage  spotting  and  falling  prematurely 
so  that  the  vitality  and  vigor  of  the  tree  is  much  reduced. 
Upon  the  fruit  it  causes  black  blotches,  first  seen  as  small 
brown  spots,  which  soon  increase  in  size  and  turn  darker 


Fig.  35.  —  Black-spot  of  the  quince,  natural  size.    After  Bailey. 

in  color.  While  this  spot  does  not  materially  injure  the 
fruit  for  use,  it  does  retard  its  full  development,  and,  be- 
cause of  impaired  beauty,  decreases  its  selling  price.  It  also, 
as  in  the  case  of  apple  scab,  gives  entrance  to  the  pink-rot 
fungus. 

The  means  of  prevention  consists  in  application  of  lime- 


72  Diseases  of  Economic  Plants 

sulfur.  Pt,epeated  trials  have  shown  that  this  is  thoroughly 
effective,  increasing  the  value  of  the  quince  crop  very  mate- 
rially both  in  size  and  quality  of  the  fruit.  The  first  applica- 
tion should  be  made  soon  after  the  blossoms  fall,  and  should 
be  followed  at  intervals  of  two  or  three  weeks  with  two  more 
treatments. 

Black-rot  (Physalospora  cydonice,  Sphceropsis) .  —  This 
rot  of  wide  distri'jution,  and  often  amounting  to  a  loss  of 
10  per  cent,  is  due  to  the  same  fungus  which  causes  black-rot 
of  the  apple,  and  the  treatments  recommended  for  the  apple 
will  prove  efficient  for  the  quince  disease.  It  has  not  yet  been 
proved  that  this  fungus  causes  cankers  on  the  quince  trees 
such  as  have  been  described  for  the  apple.  The  grower 
should,  however,  watch  carefully  for  the  presence  of  canker, 
as  the  relation  between  the  canker  and  the  rot  in  apple  indi- 
cates that  the  canker  may  possibly  be  found  on  the  quince 
also. 

Bitter-rot  {Glomerella  cingulata,  Gloeosporium) .  —  This 
disease  is  caused  by  a  fungus  identical  with  that  causing 
bitter-rot  of  the  apple.  The  treatments  already  recom- 
mended for  other  diseases  will  also  prove  efficient  here. 

European  canker  (Nectria  galligena  Bres.).  —  This  canker 
is  readily  distinguished  from  the  ordinary  cankers  pro- 
duced by  Physalospora  or  Glomerella  by  its  brilliant  red  or 
cinnamon-colored  pustules  scattered  profusely  over  the 
affected  areas.  While  cankers  due  to  this  fungus  have  been 
observed  upon  quince  in  America,  no  case  of  serious  injury 
is  known. 

Pale-rot  {Phoma  cydonice  S.  &  S.).  —  This  is  one  of  the 
most  prevalent  decays  of  quince  fruit  in  market.  The 
lesions  usually  appear  in  the  region  of  bruises  and  are  at  first 
pale  blue  or  bluish-green  in  color  and  circular  in  outline.  The 
rot  spreads  rapidly,  involving  the  entire  fruit  in  a  few  days. 
The  surface  becomes  wrinkled  and  darker  in  color.  Later 
numerous  white  fruiting  pustules  stud  the  surface  of  the 
decayed  area.  Care  in  handling  the  fruit  to  avoid  external 
injuries  is  the  only  control  measure  recommended. 


Pomaceous  Fruits 


73 


Minor  diseases 

Brown-rot,  Crown-gall,  and  Hypochnose:  see  apple. 


MEDLAR 

Though  not  extensively  cultivated  the  medlar  is  occa- 
sionally affected  with  fungi  allied  to  those  present  on  other 
pomaceous  hosts,  e.  g.  Fabrcea  mespili  (Sor.)  Atk.  causing 
leaf-blight;  Oidiuin  mespilinuin  Thiim,  and  Sclerotinia  lin- 
hartiana.   P.  &  D. 


DRUPACEOUS  FRUITS  28 

The  drupes  as  the  pomes,  comprising  highly  valuable 
individual  trees,  warrant  protective,  curative,  even  though 
expensive  measures.  The  diseases  of  the  drupes,  to  some 
extent,  are  identical  with  those  of  the  pomes,  since  both 
belong  to  the  Rosaceae.  There  are,  however,  several  im- 
portant diseases  peculiar  to  this  group  of  hosts.  The  drupes 
are  especially  sensitive  to  injury  by  fungicides,  a  fact  which 
complicates  all  questions  of  control  of  drupe  diseases  by 
spraying. 

ALMOND 

The  chief  diseases:  Yellows,  Blight,  Crown-gall,  and 
Shot-hole  are  discussed  under  peach. 

APRICOT 

The  diseases  of  the  apricot  are  essentially  those  of  the 
peach  and  will  be  more  fully  discussed  under  that  head. 
The  most  important  are:  Yellows,  less  common  than  on  the 
peach;  Phyllosticta  Shot-hole ;  Brown-rot,  especially  destruc- 
tive in  the  southwest;  Fire-blight  (Bacillus  amylovorus), 
rarely  reported'^-;  Scab,  reported  from  California,  Texas, 
and  Connecticut;  Die-back  (Valsa  leucostoma) ;  Crown-gall; 
Black-spot  {Pseudomonas  prwii),  less  troublesome  than  on  the 
peach;  Silver-leaf;  Rust,  especially  injurious  in  the  South- 
west; Coryneum  blight,^^  known  in  California,  New  York, 
Australia,  and  northern  Africa;  Frost  injury.  Gummosis  is 
not  a  specific  disease  but  a  symptom  brought  about  by  any 
one  of  various  agencies;  see  peach. 
74 


Drupaceous  Fruits  75 


CHERRY 


Leaf-spot  ^' ^^~^^  {Coccomyces  sps.,  Cylindrosporium) . — 
The  disease,  first  reported  in  Europe  in  1884,  is  widespread 
wherever  cherries  are  cultivated  and  is  usually  very  destruc- 
tive. Sweet  cherries  are  most  susceptible.  In  Ohio  the  loss 
in  one  year  was  estimated  at  $25,000.  This  disease,  on  fruit, 
pedicels,  and  leaves  is  nearly  identical  in  symptoms  with 
that  of  leaf -spot  of  the  plum.  For  description  see  p.  98. 
Diseased  refuse,  leaves,  etc.,  should  be  plowed  under  or 
destroyed.  Sour  cherry  trees  should  be  sprayed  with  lime- 
sulfur  solution  diluted  at  the  rate  of  13^  gallons  to  50  gallons 
of  water,  or  with  3-4-50  Bordeaux  mixture:  (1)  as  soon  as  the 
petals  have  fallen,  (2)  about  three  weeks  later,  (3)  directly 
after  the  fruit  is  picked.  Arsenate  of  lead,  1  pound  of  powder 
to  50  gallons  of  spray,  may  be  added  for  the  control  of  insect 
pests. 

Sweet  cherries  should  receive  the  same  treatment  as  the 
sour  except  that  lime-sulfur  solution  diluted  at  the  rate  of 
1  gallon  to  50  gallons  of  water  should  be  the  fungicide  used. 
Bordeaux  mixture  should  never  be  used  on  sweet  cherry 
trees,  because  of  the  risk  of  injury.  Dusting  has  proved 
satisfactory  in  some  localities.  The  results  of  spraying  by 
Scott  are  shown  in  the  accompanying  figures.  These  trees, 
located  in  Illinois,  were  sprayed  three  times. 
-Black-knot  (Dihotryon  morhosum). — ^As  upon  the  plum, 
this  knot  causes  serious  injury  to  the  cherry.  In  some 
sections  it  is  so  prevalent  on  the  wild  cherry  and  plum 
trees  as  to  render  control  practically  impossible,  and  in 
certain  regions  has  caused  the  abandonment  of  the  cherry- 
growing  industry.  Taken  in  time  it  is  easy  to  control.  For 
treatment  see  plum. 

Brown-rot,  mold  {Sderotinia  cinerea,  Monilia). — -The 
same  fungus  which  produces  disastrous  results  upon  the 
peach  also  causes  the  most  serious  disease  of  the  cherry,  being 
especially  destructive  on  sweet  cherries.  Several  stages  of 
its  development  are  illustrated  in  Fig.  38.     The  disease  is 


Fig.  36.  —  Unsprayed  cherry  tree  defoliated  by  leaf-spot.    After  Scott. 


Fig.  37.  — •  Cherry  tree  from  same  orcliard  shown  in  Fig.  36,  sprayed 
with  self-boiled  lime-sulfur  to  control  leaf-spot.    After  Scott. 


Drupaceous  Fruits 


77 


known  practically  wherever  the  cherry  is  grown,  and  large 
losses  are  frequent.  Fifty  per  cent  loss  was  reported  from 
New  York,  and  25  per  cent  from  Missouri  in  a  single  year. 
Treatment  is  the  same  as  for  the  peach  brown-rot. 

Curi  (Taphrina  cerasi  (Fcl.)  Sad.).  —  Cherry  curl  is 
closely  related  to  that  of  the  peach.  The  leaves  become 
wrinkled  before  they  are  full  size,  and  spores  are  produced  on 


Fig.  3S.  —  Brown-rot  showing  various  stages  of  decay.    After  Clinton. 

the  surface  of  the  leaf,  as  they  are  in  other  curls.  Instead  of 
forming  flower  buds  and  spurs,  affected  regions  develop  a 
profusion  of  twigs,  "witches'  brooms."  The  disease  is  not 
common  in  America;  but  should  it  become  so,  it  can  be  held 
in  check  by  pruning  out  the  diseased  twigs.  It  is  perennial 
in  the  twigs  and  should  be  avoided  in  budding  and  grafting. 
Powdery-mildew  ^^'  ^^  {Podosphcem  oxyacanthce  (DC.)  De 
Bary).  — This  mildew,  similar  to  that  described  in  connec- 
tion with  apple  diseases,  sometimes  does  damage  to  the 
plum  and  cherry,  especially  on  nursery  stock,  where  it  pre- 


78 


Diseases  of  Economic  Plants 


vents  either  the  growth  of  the  seeching  or  successful  budding 
or  grafting. 

On  old  leaves,  though  often  abundant,  the  fungus  does  not 
cause  great  damage,  but  when  the  attack  is  made  on  young 
growing  tips,  or  on  young  leaves,  these  delicate  structures 
suffer  greatly  from  loss  of  nourishment.  The  disease  is  com- 
mon from  the  Atlantic  to  the  Pacific. 

Unlike  most  fungi  the  mildew  grows  best  during  fair, 
diy  weather.  A  light  rain,  which  spreads  the  spores  and 
furnishes  sufficient  moisture  for  germi- 
nation, followed  by  a  dry  spell,  best 
favors  the  development  of  powdery- 
mildew. 

The  use  of  Bordeaux  mixture,  sulfur 
dust,  or  lime-sulfur  has  proved  satisfac- 
tory. Apply  about  every  ten  days  dur- 
ing the  early  growing  season;  more 
frequently,  if  necessary  to  replace  the 
poison  washed  off  by  rain. 

'  Wood-rot  ^    (Schizophyllum    alneurn 
(L.)  Schr.).  —  Small  white  specks,  the 
sporophores,    appear    upon    the    limbs 
and   trunk   in   early  summer.     In   the 
autumn   they  are  well  developed   and 
abundant ;  white  and  very  hairy,  1-3  cm. 
in  diameter,  usually  attached   on  one 
side  with  the  margins  incurved.     The 
gills  are  white,  woolly,  branched,  deeply 
split  along  the  edge,  and  revolute. 
The  affected  wood  is  brittle  and  pene- 
trated by  black  lines.    Apparently  this  disease  starts  in  roots 
injured  by  tools  during  cultivation  or  in  wounds  upon  limbs. 


Fig.  39.  —  Schizo- 
phyllum alneum, 
frequently  the 
causal  fungus  of 
wood-rot  of  cherry 
and  other  trees. 
After  Atkinson. 


Minor  diseases 

Die-back  ^^  {Vaha  leucostoma,  Cystospora).  —  The  discus- 
sion of  (lie-back  on  p.  86  is  applicable  in  this  connection. 
The  disease  is  conniion  on  the  cherry  in  the  United  States 


Drupaceous  Fruits 


79 


and  other  countries.  For  Crown-gall,  Rust,  and  Yellows, 
see  peach.  Armillaria  root-rot,  see  apple.  Blight  {Bacillus 
amylovorus)  has  been  rarely  reported  m  the  Northwest. 
Scab  is  much  less  common  than  on  the  peach.  Black-spot 
(Pseudomonas  pruni)  has  been  noted  on  the  Wragg  cherry  in 
Colorado.    See  peach. 


PEACH 

■  Brown-rot  ^''^  ^^-  ^°  (Sclerotinia  cinerea  (Bon.)   Schr.,  Mon- 
ilia).  —  Probably    no    other    disease    is    so    destructive    to 


Two  packages  of  p3ache.s,  one  healthy,  the  other  affected 
with  brown-rot.    After  Scott. 


peaches,  plums,  cherries,  and  kindred  drupes,  as  the  brown- 
rot,  which  attacks  the  fruits  as  they  approach  maturity, 


80 


Diseases  of  Economic  Plants 


turning  them  brown,  soft,  and  rendering  them  worthless. 
Aside  from  injuring  the  mature  fruit,  the  rot  attacks  the 
flowers  and  twigs.  The  disease  ranges  over  the  entire  peach- 
growing  territory,  but  is  usually  most  severe  in  the  South. 
In  some  years  the  loss  has  amounted  to  more  than  50  per  cent 
of  the  crop,  or  an  aggregate  annual  loss  of  $5,000,000.  The 
estimated  damage  in  Ohio  alone  in  one  year  was  a  quarter 
of  a  million  dollars;  in  one  year  in  Pennsylvania  twenty 
carloads  were  lost.  Apples,  pears,  and  quinces  are  attacked, 
but  to  lesser  extent. 

Its  characteristic  appearance  on  the  fruit  enables  one  to 

recognize  it  easily.    It  fir^t  appears  as  small,  circular,  brown, 

decayed  spots.    These  rapidly  en- 

1     large    until    they    embrace    the 

^P  whole  fruit,  which  at   the   same 

4^^  ^^  time    shrinks    slightly.     As   the 

j\^^^Bf  decay  advances,   small   tufts   of 

^^IJ^^I^B  ^_^  brown  threads  appear  near   the 

^^Q^^^^K^fl^k        centers  of  the  original  spots,  and 

J^^^^^^^^^^B^        spread    rapidly    until   the   whole 

^^^^^^^^^^^B  If  the  fruit  hangs  in  clusters, 

^i^^^^HpP  adjacent  fruits  begin  to  decay  at 

^^^^^  the  points  of  contact,  and  the  dis- 


FiG.  41.  —  Mummy  peach 
showing  Sclerotinia  asco 
phores.    After  Scott. 


ease  spreads  from  fruit  to  fruit  un- 
til whole  clusters  are  lost.  Fruit, 
after  it  is  picked,  may  also  suc- 
cumb to  attack,  and  peaches  that 
were  apparently  sound  at  picking  may  be  seriously  damaged 
when  they  reach  market.  Thus  the  loss  falls  upon  grower,  car- 
rier, dealer,  and  consumer.  The  decay  is  so  rapid  that  infection 
to-day  may  mean  a  totally  unsalable  peach  two  days  hence. 
Peaches  diseased  on  the  tree  may  fail  to  the  ground,  or  remain 
on  the  tree,  where  they  shrivel  and  hang  over  winter,  to  con- 
stitute the  "mummy"  peaches  so  familiar  in  infected  orchards. 
Upon  the  blossom  the  disease  is  first  evident  as  a  slight, 
brownish  discoloration,  which  spreads  rapidly,  causing  the 


Drupaceous  Fruits  81 

flower  to  wither  and  eventually  fall  off  as  a  rotten  mass, 
carrying  contagion  to  everything  in  its  path.  This  damage 
to  the  flower  is  often  confounded  with  frost  effects.  From 
the  flower  the  rot  may  spread  to  adjacent  twigs,  through 
the  flower  stalk.  Smith  states  that  the  examination  of  hun- 
dreds of  twigs  in  all  stages  of  disease  showed  that  every  one 
was  associated  with  lilighted  and  persistent  flowers.  Infec- 
tion of  the  twigs  may  also  occur  directly  from  diseased  fruit. 
Even  large  branches  may  become  seriously  cankered.  From 
repeated  observations,  however,  it  seems  probable  that 
branches  cannot  be  infected  except  through  wounds. 

The  inroads  of  this  disease  are  so  serious  that  many  peach 
and  plum  growers  have  been  obliged  either  to  secure  a 
remedy  for  this  pest  or  abandon  the  crop.  Years  in  which 
there  is  full  fruitage,  accompanied  by  damp,  warm  weather, 
are  almost  certain  to  bring  a  severe  attack.  But  it  is  not  the 
weather  which  directly  causes  the  rot;  rather  it  is  the  rapid 
development  of  the  fungus  under  proper  weather  conditions. 

The  mummified  fruits  and  cankers  serve  as  the  hibernating 
quarters  of  the  causal  fungus.  If  these  mummies  be  carefully 
observed  in  the  spring,  some  of  them  will  be  seen  to  bear 
small  stalked  disks  (Fig.  41).  These  are  the  organs  which 
furnish  spores  for  the  spring  infection. 

It  follows  that  any  practice  which  destroys  the  mummified 
fruits  lessens  the  risk  of  infection  as  does  also  the  pruning 
out  of  cankers.  Observations  by  Pollock,  ^^^  extended  over  a 
period  from  1909  to  1918,  show  that  the  sclerotia  of  the 
causal  fungus  may  remain  alive  for  at  least  ten  years,  and 
some  of  them  produce  ascocarps  every  year;  old  mummies 
or  fragments  of  mummies  giving  rise  to  smaller  spore- 
bearing  structures  than  those  formed  from  younger  sclerotia. 
In  the  light  of  these  observations  attesting  to  the  long  life 
of  the  sclerotia,  the  plowing  under  of  diseased  fruits,  here- 
tofore advised,  cannot  be  regarded  as  a  good  practice.  Ac- 
tive treatment  in  the  form  of  spraying  is  necessary.  The  most 
successful  spray  is  that  employed  by  Scott,  which  gave  the 
following  results :  — 


82 


Diseases  of  Economic  Plants 


Results  of  Experiments  for  the  Control  of  the  Peach  Brown- 
Rot,  Marshallville,  Ga.,  1908 


Peaches 

Peaches 

Plot 

Treatment 

affected  with 

Peaches 

BADLY 

Brown-Rot 

Scabbed 

Scabbed 

Per  cent 

Per  cent 

Per  cent 

1 

Lime-sulfur  wash  (15-10- 

50),  hot  water 

10. 5() 

20.75 

O.SO 

18 

Lime-sulfur  wash  (15-10- 

50),  cold  water 

12  22 

16.60 

0.60 

36 

Check  —  no  treatment. .  . 

36.98 

93.63 

42.12 

For  the  comlnned  treatment  of  peach  scab  and  brown-rot, 
at  least  three  apphcations  of  the  self-boiled  lime-sulfur, 
8-8-50,  are  necessary;  first,  when  the  petals  drop;  second, 
about  three  weeks  later;  third,  about  a  month  before  the 
fruit  ripens.  The  time  of  the  last  application  must  be  deter- 
mined by  the  ripening  date  of  the  variety.  Though  a  late 
treatment  would  be  effective  against  brown-rot,  to  avoid 
staining  the  fruit  the  last  spraying  should  be  made  a  month 
before  the  fruit  ripens.  Three  applications  are  sufficient  for 
the  Elberta  and  earlier  varieties.  A  fourth  treatment  is 
often  desirable  for  later  maturing  varieties. 

There  seems  to  be  no  question  as  to  the  advisability  of 
spraying  the  peach  orchard  where  brown-rot  and  scab  are 
troublesome,  but  other  risks  are  oftentimes  to  be  encoun- 
tered. The  curculio  and  other  insects  readily  break  the  skin 
of  the  peach  and  admit  the  brown-rot  fungus  even  through  a 
coating  of  the  spray  mixture,  so  that  a  certain  amount  of  rot 
may  always  be  expected  when  the  conditions  are  favorable. 

Scab  ^^' '^'-  (Cladosporium  carpophilum  Thtim.).  —  This 
disease,  which  is  widespread  and  so  common  that  many 
people  regard  it  as  an  integral  part  of  the  peach,  may  con- 
sist of  isolated,  sooty,  black  specks,  or  of  black  specks  so 
numerous  as  to  coalesce  into  large  blotches.  These  some- 
times cover  as  much  as  one-third  or  one-half  of  the  peach. 


Drupaceous  Fruits 


83 


The  side  which  is  attacked  is  dwarfed,  often  cracked,  and 
the  flesh  adjacent  to  the  diseased  part  is  green  and  bitter, 
even  after  the  normal  portions  are  ripe.  Leaves  and  twigs 
are  also  affected. 


Fig.  42.  —  Peach  scab.    Original. 


Scab  develops  in  most  serious  form  during  rainy  seasons, 
and  is  more  prevalent  upon  certain  late  varieties  as  Health, 
Salway,  and  Bilgen.  It  is  reported  from  Missouri  to  have 
done  damage  equal  to  70  per  cent  of  the  value  of  the  crop, 
and  Selby  estimated  the  loss  in  one  crop  in  Ohio  at  from  20  to 
50  per  cent. 


84 


Diseases  of  Economic  Plants 


Self-boiled  lime-sulfur,   8-8-50,   applied  as  indicated  for 
peach  brown-rot,  gives  excellent  results. 

-Curl  9^  (Taphrina  deformans  (Fcl.)  Tul.).*  —  Throughout 
the  peach-producing  region  this  disease  abounds,  being  par- 
ticularly injurious  in  moist  localities.  The  annual  loss 
approximates  $3,000,000  in  the  United  States. 

Curl  is  due  to  a  fungus  which  grows  in  the  leaves,  causing 
the   peculiar  malformation   which  justly   gives   rise  to   its 


Fig.  43.  —  Peach  leaf-cui 


\tkinson. 


popular  name.  This  fungus  destroys  the  utility  of  the  leaf 
as  a  starch-producing  organ,  and  eventually  causes  defolia- 
tion. This  loss  may  be  manifest  in  two  ways:  first,  by  the 
present  effect  upon  the  vitality  and  vigor  of  the  tree,  and 
immediate  injury  to  the  crop;  second,  by  a  weakening  of  the 
tree  in  succeeding  years,  due  to  the  lack  of  full  nourishment 

*  The  sub-genus  Exoascus  is  by  some  regarded  as  of  specific  rank  and 
the  name  as  Exoascus  deformans. 


Drupaceous  Fruits  85 

during  the  period  of  attack.  The  injury  in  the  present  year, 
manifest  by  a  loss  in  productiveness,  is  obvious  to  the  grower. 
The  injury  in  succeeding  years,  often  fully  as  great,  is  fre- 
quently overlooked,  or  is  not  attributed  to  its  true  cause. 

It  was  formerly  thought  that  this  fungus  persisted  in  the 
twigs  over  winter,  and  thus  lurked  ready  to  infect  the  new 
leaves  as  they  began  to  develop.  It  has,  however,  been 
proved  that  nearly,  if  not  quite,  all  spring  infection  is  due, 
not  to  perennial  mycelium,  but  to  spores  which  remain  on 
the  bark  of  the  trees. 

Prevention  of  the  disorder  lies  in  killing  these  spores  of 
the  fungus  by  winter  spraying.  For  this  purpose  Bordeaux 
mixture,  Hme-sulfur,  or  a  simple  copper-sulfate  solution 
is  efficient.  There  is  probably  little  choice  between  these 
solutions  on  the  ground  of  efficiency;  hence,  the  cost  of  the 
various  sprays  may  become  the  deciding  factor.  Lime- 
sulfur  is  preferable  when  insects  also  are  to  ])e  met.  The 
spray  should  be  applied  from  one  to  three  weeks  before  the 
buds  open  in  the  spring,  and  thoroughness  should  be  the 
chief  aim.  Spraying  should  be  done  in  dry,  calm  weather, 
during  the  middle  of  the  day,  in  order  to  avoid  dew  or  frost 
upon  the  limbs. 

Pierce  states  that  as  a  result  of  the  treatment  of  peach 
curl  in  California,  from  95  to  98  per  cent  of  the  spring 
foliage  was  saved.  A  net  gain  of  600  per  cent  in  the  foliage 
over  that  retained  by  adjoining  unsprayed  trees  resulted 
in  the  case  of  several  different  sprays.  Bordeaux  mixture, 
when  applied  to  the  dormant  tree,  increased  the  weight  and 
starch-producing  power  of  the  leaves,  and  the  sprayed  trees 
showed  great  gain  over  the  unsprayed  in  the  number  and 
quality  of  the  fruit  buds  which  they  produced  for  the  follow- 
ing year.  The  gain  in  the  numl)er  of  spur  buds  was  over 
100  per  cent  in  some  cases.  The  sprayed  trees  also  produced 
more  vigorous  growth  of  new  wood,  the  wood  to  produce  the 
crop  for  the  next  year.  Thus,  in  one  experiment  the  spring 
growth  of  the  unsprayed  tree  averaged  7.85  inches;  on  the 
sprayed  trees  it  was  24.75  inches.     The  average  value  of 


86  Diseases  of  Economic  Plants 

fruit,  per  tree,  in  rows  treated  with  the  most  effective  Bor- 
deaux mixture  ranged  as  high  as  $6.20  above  that  in  ad- 
joining untreated  rows,  or  the  equivalent  of  a  net  gain  of 
$427.80  per  acre.  Over  one  thousand  per  cent  net  gain  in  the 
set  fruit  has  resuhed  from  the  use  of  some  of  the  more  effec- 
tive sprays. 

The  trees  should  be  sprayed  each  season,  since  experi- 
ments prove  that  treatment  one  season  will  not  prevent  the 
disease  the  following  year.  Spraying  should  he  done  even 
though  the  trees  are  not  expected  to  liear,  since  the  loss  of 
the  crop  of  leaves  is  as  great  a  drain  upon  the  trees  as  is  the 
maturing  of  one-half  to  two-thirds  of  a  crop  of  fruit. 

Die-back^'*  (Valsa  leucostoma  (Pers.)  Fr.,  Cytospora). — 
This  disease  of  limbs,  trunk,  and  twigs  was  first  fully  de- 
scribed in  the  United  States  by  Rolfs  of  Missouri  in  1907  who 
noted  it  upon  peach  and  Japanese  plum.  It  is  present  also  in 
Europe  and  Australia. 

Infection  occurs  upon  buds  or  wounds  during  the  growing 
season,  and  in  early  winter  and  spring  the  tips  of  young 
branches,  especially  water  sprouts,  are  killed  back  from  2.5 
to  46  cm.  As  many  as  300  such  dead  twigs  have  been  noted 
on  a  single  tree.  It  develops  most  rapidly  in  a  warm  spell 
following  freezing  weather  in  the  spring,  and  is  more  serious 
upon  trees  that  have  been  weakened  by  other  causes. 

Twigs  killed  during  the  winter  show  at  first  a  dark  pur- 
plish skin,  changing  later  to  leathery,  scarlet,  or  purple, 
finally  drab.  Then  the  skin  loosens  and  wrinkles.  At  this 
time  black  pycnidia  appear  under  the  skin.  These  soon 
push  out  a  white  cap  through  a  transverse  slit  in  the  skin, 
and  in  wet  weather  exude  very  fine,  red  threads  of  spores. 
Gum  flow  usually  accompanies  the  constriction,  marking 
the  juncture  of  dead  and  healthy  wood.  During  summer, 
leaves  on  infected  twigs  frequently  wilt,  owing  to  the  gir- 
dling of  the  stem.  Upon  the  trunk  large  wounds,  often 
regarded  as  sun  scald,  are  produced,  while  upon  young  limbs 
the  wounds  appear  as  enlargements  or  "knots."  Large 
limbs  or  even  whole  trees  succumb. 


Drupaceous  Fruits  87 

Excision  should  be  practiced.  Spraying  lessens  the  disease 
but  is  not  wholly  effective. 

Coryneum-blight '^^' ^'^  {Coryneum  heijennckii  Oud.).  ^ 
First  noted  by  Pierce  and  fully  descriljed  by  Smith,  Cory- 
neum-blight,  troublesome  in  California  for  years,  has  been 
observed  as  far  east  as  New  York,  also  in  Europe  and  Aus- 
tralia. 

The  symptoms  are  djdng  of  the  buds  of  fruiting  wood, 
spotting  of  green  twigs,  and  dropping  or  underdevelopment 
of  young  leaves  antl  fruit,  accompanied  l)y  gimimy  exudate, 
especially  upon  the  one-year-old  fruiting  twigs.  Leaves 
opening  from  buds  which  survive  the  disease  are  marked  by 
small  dead  areas  of  tissue,  which  soon  fall  out,  leaving  "shot 
holes."  It  is  essentially  a  winter  or  early  spring  disease  of 
fruiting  twigs  and  one-year-old  wood,  and  the  principal  dam- 
age is  from  death  of  buds  and  twigs  before  the  fruit  de- 
velops.   Infection  occurs  in  winter  before  new  growth  begins. 

Pruning,  followed  by  spraying  with  Bordeaux  mixture  or 
other  dormant  sprays,  during  the  early  winter  (in  California 
between  November  1  and  December  15),  produces  best 
results. 

•  Crown-gall  and  Hairy-root  ^*'  ^°-' """  (Pseudomonas  tume- 
faciens  EFS.).  — Crown-gall  causes  a  tumor-like  outgrowth 
near  the  ground  line  on  certain  trees  and  shrubs  (Fig.  44), 
particularly  upon  members  of  the  rose  family,  pomes,  drupes, 
raspberries,  etc.  Hairy-root  consists  of  a  profuse  develop- 
ment of  small  tufts  of  fine  roots. 

Careful  cross  inoculations  by  Hedgcock,  using  fragments 
of  galls,  have  demonstrated  that  crown-gall  of  the  almond, 
apricot,  blackberry,  cherry,  peach,  plum,  prune,  chestnut, 
and  walnut  are  intercommunicable.  It  has  also  been  demon- 
strated by  Smith  and  Townsend  that  crown-gall  of  the  peach 
tree  as  well  as  of  tomato,  potato,  tobacco,  beet,  hop,  carna- 
tion, grape,  raspberry,  and  apple  can  be  produced  by  inocula- 
tion with  Pseudomonas  tumefaciens,  also  that  the  organisms 
of  the  peach,  apple,  hop,  rose,  and  chestnut  galls  are  inter- 
changeable. 


Diseases  of  Economic  Plants 


In  addition  to  the  above-named  plants,  natural  galls  on 
quince,  plum,  dewberry,  raspberry,  corn,  turnip,  salsify, 
parsnip,  lettuce,  radish,  cotton,  alfalfa,  clover,  pecan,  willow, 


Fig.  44.  —  Peach  crown-gall.    After  Hedgcock. 

poplar,  chrysanthemum,  honeysuckle,  euonymus,  arbutus, 
marigold,  pyrethrum,  peony,  and  oleander  have  been  studied, 
while  a  complete  list  of  susceptible  plants  would  include 
many  more.  The  disease  in  a  form  known  as  soft-gall  is 
found  commonly  on  herbaceous  plants  or  cane  fruits. 


Drupaceous  Fruits  89 

On  many  plants  crown-gall  is  practically  harmless,  while 
on  others,  especially  the  fruit  and  nut  trees  and  the  cane 
fruits,  it  is  injurious.  The  chief  injury  seems  to  arise  from 
the  fact  that  crown-gall  paves  the  way  for  the  entrance  of 
rot-producing  parasites,  interferes  with  proper  root  develop- 
ment and  the  conduction  of  foods  and  water.     Whatever 


Fig.  45.  —  Cracked  peach,  caused  by  Pseudomonas 
■pruni.  Advanced  stage  on  fruit  nearly  ripe. 
After  Roberts. 

may  be  the  actual  mode  of  producing  injury,  the  fact  is  well 
estabHshed  that  trees  with  crown-gall  do  not,  in  general, 
develop  or  yield  as  well  as  trees  without  galls,  though  in  rare 
cases,  trees  with  crown-gall  may  fully  equal  ungalled  trees. 
All  diseased  stock  should  be  avoided,  as  well  as  stock  from 
nurseries  where  the  disease  is  known  to  exist.  Care  on  the 
part  of  nurserymen  to  use  soil  free  from  crown-gall;  to  avoid 
wounding  the  young  trees  and  to  make  close-fitting  grafts, 
and  protect  them  well  with  wax,  will  lessen  infection. 


90 


Diseases  of  Economic  Plants 


Black-spot  ^^^  ^"^  {Pseudomonas  pruni  EFS.).  —  Peaches, 
plums,  apricots,  nectarines,  and  more  rarely  cherries  are 


I'lG.  46.  —  Peach  leaves  inoculated  with  culture  of  Pseudoinottds  pruni. 
Photograph  taken  43  days  after  inoculation.    After  Eolfs. 


susceptible  to  black-spot,  affecting  chiefly  the  leaves,  but 
occurring,  also,  on  fruit  and  branch.  It  constitutes  a  really 
serious  disease  on   peaches,   being  next  in   importance  to 


Drupaceous  Fruits  91 

brown-rot  and  scab,  and  occurs  in  the  Eastern  and  Central 
United  States,  though  unknown  outside  of  the  United  States. 
It  was  first  noted  about  1903. 

Spots  first  appear  on  the  leaves  as  small,  gray  specks  which 
soon  become  angiilar  and  water-soaked,  later  brown.  Single 
spots  measure  1-5  mm.  in  diameter.  The  diseased  tissue 
usually  drops  out,  leaving  "shot-holes."  Badly  diseased 
leaves  fall  and  a  large  percentage  of  defoliation  is  common. 
On  twigs,  water-soaked  spots  surrounding  the  lenticels 
appear,  developing  to  a  length  of  four  centimeters  or  more. 
The  diseased  areas  become  sunken  and  brown  in  age,  and 
often  develop  into  perennial  cankers.  On  fruit,  the  specks 
are  at  first  similar  to  those  on  the  leaves,  but  the  skin  soon 
breaks  and  cracks  appear.    (Fig.  45.) 

Trees  that  are  kept  in  good  growing  condition  by  proper 
pruning  and  cultivation  are  not  seriously  injured  by  black- 
spot. 

Powdery-mildew  {Podosphcera  oxyacanthce  (DC.)  De  Bary, 
and  S'phcerotheca  pannosa  (Wallr.)  Lev.).- — ^  These  wide- 
spread mildews,  in  general  appearance,  are  similar  to  the 
powdery-mildew  of  the  grape,  cherry,  lilac,  and  rose.  Some- 
times the  attack  is  so  general,  on  twig,  leaf,  and  fruit  as  to 
practically  destroy  the  crop.  When  on  fruit,  the  mildew  ap- 
pears first  while  the  peach  is  small,  causing  irregular,  grayish, 
moldy  blotches.     As  these  enlarge,  cracks  often  develop. 

Sulfur  may  be  used  as  a  dust,  or  a  lime-sulfur  spray,  1-50, 
may  be  applied.  Treatment  should  be  made  as  soon  as  the 
mildew  is  seen.    Two  or  three  treatments  may  be  required. 

Yellows. ^°^'  ^^"^  ^^"  —  Peach  yellows  has  been  known  in  the 
United  States  since  1760.  From  a  region  near  Philadelphia, 
as  a  center,  it  has  spread  until  now  it  is  known  throughout  a 
large  territory  embracing  Virginia,  Arkansas,  Texas,  and 
Canada,  and  is  constantly  extending  its  frontier  in  every 
direction.  It  is  not  known  to  occur  outside  of  North  America. 
The  disease  is  of  unknown  origin,  but  it  has  been  proved 
beyond  question  that  it  is  contagious.  The  roots  of  diseased 
plants,  however,  do  not  infect  the  soil,  and  trees  may  safely 


92  Diseases  of  Economic  Plants 

be  set  in  the  places  from  which  diseased  trees  have  been 
removed. 

Recognition  marks,  which  leave  no  uncertainty  as  to  its 
identity,  are  described  by  Smith  as  follows:  "Prematurely 
ripe,    red-spotted   fruits,    and   premature   unfolding   of   the 
leaf  buds  into  slender,  pale  shoots,  or  into  branched,  broom- 
like growths,  are  the  most  characteristic 
symptoms  of  yellows.    The  time  of  ripen- 
ing of  premature  fruit  varies  within  wide 
limits;   sometimes  it  precedes  the  nor- 
mal ripening  by  only  a  few  days,  and  at 
other  times  liy  several  weeks.    The  red 
spots  occur  in  the  flesh  as  well  as  on  the 
skin,  making  the  peach  more  highly  col- 
ored than  is  natural.    The  taste  of  the 
Fig    47.  —  Mildew    ^^""^^  ^^  generally  inferior  and  often  in- 
upon  peach  fruit,     sipi^l,    mawkish,    or   bitter.     Often  this 
After  Bailey.  premature  ripening  is  the  first  sjanptom 

of  yellows.  The  peaches  are  then  of  good 
size  and  quite  showy,  and  occur  on  trees  in  full  vigor,  upon 
limbs  bearing  abundant  green  foliage,  and  sometimes  also 
other  fruits  which  afterward  ripen  normally. 

"Often  during  the  first  year  of  the  disease  this  kind  of  fruit 
is  restricted  to  certain  limbs,  or  even  to  single  twigs,  which, 
however,  do  not  differ  in  appearance  from  other  limbs  of  the 
tree.  The  following  year  a  larger  part  of  the  tree  becomes 
affected  and  finally  the  whole  of  it,  the  parts  first  attacked 
now  showing  additional  symptoms,  if  they  have  not  already 
done  so.  These  symptoms  are  the  development  of  the 
winter  buds  out  of  their  proper  season.  Like  the  prematur- 
ing  of  the  fruit,  the  date  of  this  also  varies  within  wide  limits. 
The  buds  may  push  into  shoots  only  a  few  days  in  advance 
of  the  proper  time  in  the  spring,  or  may  begin  to  grow  in 
early  summer,  soon  after  they  are  formed,  and  while  the 
leaves  on  the  parent  stem  are  still  bright  green.  This  is  a 
very  common  and  characteristic  symptom,  and  is  especially 
noticeable  in  autumn  when  the  normal  foliage  has  fallen. 


Fig.  48.  —  Peach  tree  showing  yellows.    After  Sheldon. 


94  Diseases  of  Economic  Plants 

Usually  under  the  influence  of  this  disease  feeble  shoots  also 
appear  in  considerable  numbers  on  the  trunk  and  main 
limbs.  These  arise  from  old  resting  buds,  which  are  buried 
deep  in  the  bark  and  wood,  and  remain  dormant  in  healthy 
trees.  Such  shoots  are  sometimes  unbranched,  and  nearly 
colorless,  but  the  majority  are  green  and  repeatedly  branched, 
making  a  sort  of  broomlike,  erect,  pale  green,  slender  growth, 
filling  the  interior  of  the  tree." 

A  tree  exliibiting  these  symptoms  should  be  cut  and 
burned.  It  is  valueless,  and  its  presence  is  a  serious  menace 
to  the  owner  as  well  as  to  the  country  at  large. 

Rosette.^'^^"^^''  —  The  peach  rosette  is  southern  in  distribu- 
tion, being  known  chiefly  in  Georgia  (where  it  was  first 
noted  in  1879),  South  Carolina,  and  Kansas.  As  to  its  na- 
ture, means  of  spread  and  prevention,  precisely  what  has 
been  said  of  yellows  applies.  Its  distinguishing  characters 
are  given  by  Smith  as  follows :  — 

"Rosette  clearly  belongs  to  the  same  type  of  diseases  as 
yellows,  but  its  first  stages  are  more  striking  and  its  prog- 
ress is  much  more  rapid.  It  may  first  attack  part  of  the 
tree  and  then  the  remainder,  the  same  as  the  yellows,  but 
it  is  more  likely  to  appear  at  once  on  the  whole  tree,  and 
generally  in  early  spring.  In  trees  attacked  in  this  manner, 
all  of  the  leaf  buds  grow  into  compact  tufts  or  rosettes. 
These  rosettes,  though  seldom  more  than  two  or  three  inches 
long,  usually  contain  several  hundred  small  leaves.  A  tree 
thus  attacked  always  dies  during  the  following  winter  or 
autumn.  When  part  of  a  tree  is  thus  attacked,  that  part 
dies  as  above  described,  and  the  remainder  shows  symptoms 
the  next  spring,  to  die  in  turn  after  about  six  months. 

"The  prevailing  color  of  the  foliage  is  yellowish  green  or 
olivaceous.  The  older  leaves  at  the  base  of  the  tufts  are 
largest,  and  frequently  grow  to  a  length  of  several  inches, 
but  have  inrolled  margins  and  a  peculiar  stiff  appearance, 
due  to  the  fact  that  they  are  straighter  than  healthy  leaves. 
These  outer  leaves  turn  yellow  in  early  summer  and  drop 
as  readily  as  though  it  were  autumn,  while  the  inner  leaves 


Drupaceous  Fruits  95 

of  the  rosette  are  still  green  and  delicate.  The  compact 
bunching  of  the  leaves  is  very  conspicuous,  and  makes  the 
trees  look  quite  unlike  those  affected  by  yellows.  Where  a 
tree  is  attacked  in  all  parts,  it  matures  no  fruit.  In  all  the 
cases  which  have  been  noticed  the  fruit  borne  by  affected 
trees  either  shrivels  while  green  and  drops  off,  or  else  ripens 
naturally. 

"In  the  absence  of  premature,  red-spotted  fruit,  in  the 
severity  of  the  disease  from  the  outset,  and  in  its  rapid 
progress,  it  is  quite  unlike  yellows,  which  is  decidedly  chronic, 
and  the  first  slight  symptoms  of  which  usually  occur  in  very 
green  and  thrifty  trees,  and  are  frequently  overlooked  the 
first  season." 

The  treatment  is  to  cut  and  burn  infected  trees.  No  care- 
lessness should  be  tolerated  as  regards  this  disease  or  yellows. 

Little-peach. ^^^"^^^  —  This  seems  first  to  have  been  pub- 
licly noted  by  Smith  in  an  address  in  Michigan  in  1898,  in 
which  state  it  had  been  of  alarming  character  prior  to  1893; 
since  these  years  it  has  appeared  in  New  York,  New  Jersey, 
and  Canada.  The  most  prominent  symptom  is  small,  un- 
developed fruit,  one-half  to  one-third  the  usual  diameter, 
ripening  some  10  to  14  days  later  than  normal  fruit,  and 
having  "stringy"  flesh  and  insipid  or  bitter  flavor.  The 
somewhat  drooping  leaves  are  small,  one-half  normal  size, 
and  vary  from  light  green  to  yellowish-green.  An  orchard 
once  affected  is  of  no  further  value,  and  should  be  removed 
and  lun-ned  because  of  the  danger  of  contagion. 

Frost  Injury.  —  Peaches  are  especially  susceptible.  For 
discussion,  see  apple. 

Minor  diseases 

Pustular-spot  ^"'  (Hehninthosporium  carpophilum  Lev.).  — 
Peaches  affected  with  this  disease  are  described  by  Selby  as 
"Badly  disfigured,  having  numerous  pimply  red  spots  with 
light  brown  centers."  Upon  yellow  varieties  the  pustule  is 
commonly  lacking,  there  being  simply  a  light  brown  center 
with  a  red  border.    As  the  fungus  which  causes  this  spot  rests 


96  Diseases  of  Economic  Plants 

purely  upon  the  surface  its  development  may  be  prevented 
by  spraying.  Selby  reduced  the  injury  from  16  per  cent  to 
1  per  cent  by  three  applications  of  Bordeaux  mixture. 

Rust  {Transchelia  punctata  (Pers.)  Arth.).  —  A  true  rust 
exists  upon  the  peach,  plum,  and  cherry  and  near  kin.  While 
more  common  upon  the  plum,  it  very  frequently  does  damage 
to  the  peach,  in  some  cases  being  so  serious  as  to  cause  almost 
complete  defoliation.  The  alternate  stage  is  not  uncommon 
upon  the  hepatica  in  the  spring. 

This  malady  will  be  recognized  by  the  presence  of  small, 
round,  dusty  sori  on  the  lower  surface  of  the  leaves  and  on 
the  young  shoots,  while  in  the  inunediate  region  of  these 
spore-bearing  pustules,  the  leaf,  seen  from  above,  often 
presents  a  reddish  or  reddish  yellow  color. 

Stem-blight  (Phoma  yersicce  Sacc).  —  A  fungus  on  the 
bark  which  fructifies  in  minute  pustules  sometimes  causes 
twigs  to  die.  The  disease  may  be  recognized  by  the  dead 
bark  thickly  studded  with  small  pycnidia.  Burning  the 
diseased  branches  will  prevent  spread  of  the  pest. 

Frosty-mildew  (Cercosporella  persica  Sacc).  —  In  damp, 
shaded  localities,  especially  on  trees  of  dense  foliage,  a  disease 
occurs  in  the  form  of  pale-yellowish  leaf  spots.  These  show, 
on  the  underside,  a  delicate  frostlike  appearance,  due  to  the 
growth  of  white  spore-bearing  hyphse.  It  is  not  usually 
serious,  though  widespread,  and  sprays  recommended  else- 
where suffice  to  hold  frosty-mildew  in  check  also. 

Cercospora  shot-hole  {Cercospora  circumscissa  Sacc).  — 
This  is  very  widespread,  producing  spots,  or,  when  the 
diseased  tissue  falls  out,  oval  holes,  in  the  leaves.  It  also 
infects  small  branches.  The  chief  injury  lies  in  destruction 
of  leaf  tissue  and  of  valuable  shoots.  Dormant  spraying 
recommended  for  the  curl  is  useful  here.  Phyllosticta  shot- 
hole  {Phyllo.siida  circumscissa  Cke.).  —  Similar  in  appearance 
and  effect  to  Cercospora  shot-hole,  it  responds  to  like  treat- 
ment. Armillaria  and  Clitocybe  root-rots,  see  apple;  Silver- 
leaf,  see  plum. 


Drupaceous  Fruits 


97 


PLUM 

•  Black-knot  ^^^  (Dibotryon  morbosum  (Schw.)  T.  &  S.).  — 
The  black-knot  receives  its  name  from  the  swollen  black 
distortions,  3-15  cm.  long,  upon  the  branches.  In  a  young 
condition  the  galls  are 
olivaceous,  but  as  the 
season  advances  they 
become  darker  and 
eventually  coal  black. 
At  the  same  time  soft 
tissue  changes  to  a 
hard,  brittle  texture. 

When  the  knot  com- 
pletely encircles  the 
twig,  the  supply  of 
nourishment  to  more 
distant  parts  is  seri- 
ously interfered  with. 
If  less  than  the  whole 
of  the  circumference 
be  involved,  the  dam- 
age is  not  so  great, 
but  it  is  even  then  suf- 
ficient to  seriously  im- 
pair the  fruiting  of  the 
tree.  Black-knot  may 
either  kill  the  tree  in 
a  year  or  two,  or  sim- 
ply destroy  its  value. 
All  varieties  of  plums, 
and  nearly  all  cherries, 
are  subject  to  the  dis- 
ease, which  is  therefore  very  widely  distributed.  It  is  more 
common  in  the  East  than  in  the  West. 

It  is  probable  that  infection  can  occur  only  through  injured 
bark.     One  step  toward  lessening  the  disease  is,  therefore, 


Fig.  49.  —  Portion  of  a  plum  tree  badly 
infested  with  black-knot.     Original. 


98  Diseases  of  Economic  Plants 

to  exercise  all  care  not  to  bruise  the  tree.  An  effective  meas- 
ure, however,  consists  in  pruning  out  and  burning  all  black 
knots.  This  course,  if  followed  persistently  and  thoroughly, 
will  remove  all  danger.  Experiments  show  that  spraying 
very  materially  lessens  the  spread  of  black-knot,  and  while  it 
might  not  pay  to  spray  to  prevent  this  disease,  spraying  in 
an  orchard  for  other  reasons  really  diminishes  this  risk. 

Plum-pockets  i^^'  ^^^  (Taphmia  pruni  (Fcl.)  Tul.  and  T. 
communis  (Sad.)  Gies.). — The  disease  is  widespread  in 
Europe  and  the  United  States,  and  in  certain  localities  it  is 
destructive.  The  name  "plum-pocket,"  or  "plum-bladder," 
arises  from  the  curious  hollow  deformity  of  the  plum,  which 
appears  soon  after  the  flowers  fall.  The  pulp  and  stone  of 
the  fruit  are  replaced  by  a  thin,  soft,  inflated  shell,  and  in 
place  of  the  seed,  merely  a  hollow  cavity  exists.  The  affected 
fruits  vary  from  2-5  cm.  in  length,  and  can  readily  be  dis- 
tinguished from  the  healthy  fruit  by  their  pale  yellow  color. 
As  they  age,  they  become  coated  over  with  a  fine  powder,  the 
spores  of  the  fungus.    Later  the  pockets  turn  black  and  fall. 

The  attack  of  the  fungus  is,  to  some  extent,  local  in  char- 
acter; thus  a  single  tree  in  an  orchard  may  bear  "pockets," 
sometimes  every  fruit  on  the  tree  being  affected,  while  sur- 
rounding trees  are  normal.  A  tree  once  affected  may  con- 
tinue to  bear  pockets  in  succeeding  years.  Treatment,  in 
such  cases,  consists  in  cutting  and  burning  the  affected 
branches  or  trees.  To  some  extent  the  disease  is  also  due  to 
yearly  surface  infection,  which  may  be  prevented  by  spraying 
as  for  peach  curl. 

Leaf-spot  ^^"^^  (Coccomyces  prunophorce  Higg.,  Cylindro- 
sporium) .  —  Leaf -spot  or  shot-hole  disease,  similar  to  that  of 
plums  and  cherries,  produces  discoloration  of  the  leaf  tissue, 
the  spot  often  bearing  a  red  or  purple  border.  If  abundant 
several  spots  may  coalesce  as  they  enlarge.  The  tissue  in- 
volved dies,  turns  brown,  and  eventually  drops  from  the 
leaf,  leaving  circular  or  ragged  holes.  The  disease  is  also 
frequent  upon  petioles. 

The  attack  is  insidious,  and  the  disease  often  does  much 


Drupaceous  Frait.  99 

damage  before  its  presence  is  really  known.  Defoliation  is 
the  chief  injury.  This  checks  starch  production,  and  thus 
impairs  the  tree's  general  vigor  and  productiveness,  even 
weakening  the  tree  to  such  an  extent  that  it  cannot  with- 
stand the  winter.  As  high  as  80  per  cent  damage  has  been 
reported.  The  loss  in  Ohio  was  estimated  as  $20,000  in  one 
year.  Leaf -spot  is  especially  injurious  to  nursery  stock,  as 
it  may  interfere  with  successful  budding  and  grafting.  For 
treatment,  see  cherry. 

Scab  {Cladosporium  carpophilum  Thiim.).  —  Plum  scab 
appears  as  spots  on  the  fruit,  similar  to  the  scab  of  peaches. 
When  plums  begin  to  I'ipen  or  are  just  turning  in  color,  small 
round  patches,  pale-greenish  or  grayish  in  color  and  not 
larger  than  the  head  of  a  pin,  develop.  These  increase  in 
size,  in  some  cases  to  a  centimeter  in  diameter.  In  older 
specimens  the  diseased  spots  are  frequently  confluent  and  of 
darker  brown  color.  In  very  old  specimens,  especially  where 
the  fruit  has  undergone  decomposition,  the  patches  become 
black  and  uneven. 

Treatment  identical  with  that  recommended  for  peach 
scab  will  apply  in  this  case. 

Wilt  ^^^  {Lasiodiplodia  triflorce  Hig.).  —  Restricted  to 
the  Japanese  plum  and  hybrids,  this  injurious  wilt  has  thus 
far  been  observed  only  in  Georgia,  North  Carolina,  and 
Alabama.  Often  the  first  symptom  is  a  sudden  wilting  of  the 
leaves  of  a  single  branch  or  of  a  whole  tree.  At  the  base  of 
the  wilted  portion,  the  bark  and  cambium  are  dead  and  the 
wood  brown  or  black.  The  entire  tree  usually  dies  within  a 
year  from  the  first  observable  wilt.  The  causal  fungus  ap- 
pears to  gain  entrance  to  the  host  only  through  wounds,  and 
in  the  tree  lives  chiefly  in  the  ducts.  This  disease,  therefore, 
presents  a  case  with  very  few  parallels,  i.  e.  of  a  tree  killed  by 
plugging  of  the  veins  by  fungi.  Prevention,  by  avoiding 
wounds,  or  by  disinfecting  them  when  they  occur,  is  the  only 
recourse. 

Silver-leaf  (Stereum  purpureum  Fr.).  — The  leaves,  though 
normal  in  size  and  form,  take  on  an  ashen  gray  luster,  this 


w(v^,..*%^ 

wmm&mr^  ^.^v. 

^-W/M 

Fici.  50.  —  Plum  wilt.     After  Higgins. 


Drupaceous  Fruits  101 

symptom  showing  first  on  single  branches  and  extending 
year  by  year  till  the  whole  tree  is  involved.  The  twigs  first 
infected  soon  die,  and  in  the  course  of  a  few  years  the  whole 
tree  usually  succumbs.  The  wood  of  diseased  branches  is 
browned.  The  sporophores  of  the  Stereum,  which  appears 
to  be  the  usual  causal  agent,  develop  only  after  the  death 
of  the  tree.  The  disease  is  most  common  on  plum  and  other 
drupes,  but  is  known  also  on  apple,  pear,  currant,  goose- 
berry, chestnut,  and  ash. 

Brown-rot  {Sclerotinia  dnerea,  Monilia). — Brown-rot  is 
serious  on  the  plum  as  it  is  with  the  peach  and  cherr3^  The 
loss  in  Ohio  in  one  year  was  estimated  at  $25,000. 

For  description  and  treatment,  see  peach. 

Minor  diseases 

Blight  ^^'^  {Bacillus  amylovorus).  —  Blight  of  the  apple 
and  pear  has  been  discussed  on  preceding  pages.  A  similar 
blight  is  rarely  known  to  affect  the  plum  tree,  and  careful 
studies  by  Jones  show  that  the  diseases  on  plum  and  pear  are 
identical.  For  treatment,  see  pear.  For  Powdery-mildew, 
see  cherry.  Crown-gall,  Armillaria  root-rot,  Rust,  Black- 
spot  (Pseudomonas  primi),  see  peach.  Yellows  and  Rosette 
are  less  injurious  than  on  peach;  Little-plum  is  similar  to 
Little-peach. 


SMALL  FRUITS  ^s 

BLACKBERRY,  DEWBERRY,  RASPBERRY 

The  disease  of  these  three  crops,  of  the  genus  Rubus,  are 
so  nearly  identical  that  they  may  be  treated  under  one 
caption. 

Anthracnose  'i^-i^o,  150  [Plectodiscella  veneta  Burk.,  GIobo- 
sporium) .  —  The  anthracnose,  on  both  blackberries  and 
raspberries,  is  one  of  the  most  serious  and  widely  distributed 
diseases  of  these  crops.  The  first  publication  in  America 
regarding  it  seems  to  have  been  made  in  1882  by  Burrill. 
Since  then  numerous  papers  from  many  sections  attest  its 
importance.  In  1907  it  was  estimated  to  have  injured  one- 
third  of  the  crop  in  Nebraska,  one-half  in  Wisconsin,  and 
even  more  in  Illinois.  The  chief  seat  of  attack  is  the  cane, 
especially  upon  young  stalks,  though  the  disease  appears 
also  upon  both  petioles  and  leaves. 

The  fungus  often  appears  upon  young  canes  before  they 
are  25  cm.  high,  making  small,  purplish  spots,  which  soon 
become  grayish  or  dirty  white  in  the  centers.  The  borders  of 
the  spots  are  purplish  and  slightly  raised.  Later  as  the  spots 
enlarge  they  coalesce,  making  irregular  blotches  2  cm.  or 
more  long,  which  often  encircle  the  cane.  The  stalk  then 
withers  and  dies  from  lack  of  sap  supply.  Badly  diseased 
canes  present  a  bark  of  rough,  scabby  appearance  due  to  the 
efforts  of  the  cane  to  heal  the  wound.  Canes  occasionally 
crack  from  this  disease.  The  chief  injury  is  to  the  cambium 
layer  or  the  sappy  outer  wood.  The  leaves  on  affected  canes 
are  dwarfed,  the  fruit  ripens  prematurely,  is  undersized,  and 
often  dries  up. 

Upon  the  petioles  of  the  older  leaves  the  disease  appears 
early,  spreading  thence  along  the  ribs  to  the  leaf.  Owing 
to  the  one-sided  attack  upon  the  veins  and  petioles,  the 
102 


Small  Fruits 


103 


leaves  develop  unequally, 
often  with  inrolled  edges. 
Upon  the  lower  surface  very 
small  spots  about  1  mm.  in 
diameter  are  produced,  from 
which  the  diseased  tissue 
often  falls.  In  the  older 
diseased  spots  the  spore- 
bearing  acervuli  are  just 
visible  to  the  naked  eye. 

Occasionally,  an  incipient 
attack  may  escape  observa- 
tion during  the  first  and 
second  years,  and  even  well 
into  the  third  year.  Then, 
with  prospect  of  a  good 
yield,  the  berries  shrivel  on 
the  stems  and  later  many 
plants  die.  More  often  the 
disease  remains  moderately 
injurious  from  year  to  year, 
weakening  the  plants  and 
diminishing  the  yield. 

In  localities  subject  to 
this  disease,  it  is  best  to 
rotate  crops  so  as  to  avoid 
keeping  raspberries  or 
blackberries  more  than 
three  years  on  the  same 
soil,  and  to  set  out  only 
healthy  plants.  When  the 
disease  appears,  cut  out  and 
burn  diseased  parts  immedi- 
ately after  picking.  Spray- 
ing with  lime-sulfur  is  effective.  Use  three  applications, 
(1)  before  the  leaves  appear,  1-20,  (2)  when  the  shoots  are 
six  inches  high,  1-50,  (3)  just  before  blossoming. 


Fig.  51.  —  Anthracnose  on  black 
raspberry,  showing  typical  fis- 
sures.    After  Burkholder. 


104  Diseases  of  Economic  Plants 

Crown-gall  {Pseudomonas  tumcfaciens).  —  Frequently 
swellings  are  noticed  on  the  stems  near  the  roots,  or  even  on 
the  higher  parts  of  stems,  of  the  raspberry  or  blackberry 
sufficiently  numerous  to  injure  the  health  of  the  plant. 
These  galls  are  apparently  of  the  same  nature  as  the  crown- 
gall  of  the  peach,  almond,  apple,  etc.  It  is  desirable  to 
pull  up  and  destroy  diseased  plants  and  avoid  placing  black- 
berries and  raspberries  on  ground  which  is  known  to  be 
infected. 

Leaf-spot  (Septoria  ruhi  West.).- — Upon  the  leaves  of 
blackberries,  raspberries,  and  dewberries  small  spots  fre- 
quently appear,  having  a  central  region  white  or  ashen  in 
color,  and  the  border  brown  or  often  of  reddish  tint.  These 
spots  are  about  3  mm.  in  diameter.  Close  examination  of 
the  central,  ashen  area,  especially  with  a  hand  lens,  reveals 
exceedingly  small,  black  pycnidia  scattered  throughout. 

While  this  disease  is  exceedingly  common  and  of  wide 
distribution,  it  does  not  often  develop  an  epidemic  and  usually 
does  but  little  injury,  though  its  damage  has  been  estimated 
as  high  as  20  per  cent  in  Florida  and  Ohio.  No  treatment 
has  yet  proved  of  sufficient  value  to  warrant  its  use. 
-  Orange-rust  ^-^  (Gijmnoconia  inter stitialis  (Schlecht) 
Lager.).  —  In  the  early  spring  the  under  sides  of  the  leaves 
of  blackberries  and  raspberries  often  present  a  livid  red  or 
orange  color.  This  rust  was  observed  as  early  as  1817,  in 
Kamchatka,  and  is  very  widely  distributed  in  the  LTnited 
States,  Europe,  and  Asia,  upon  some  nine  species  of  Rubus, 
both  cultivated  and  wild.  It  is  known  from  Maine  to 
Minnesota  and  Florida  to  California,  and  is  in  some  cases 
very  destructive. 

Examination  of  a  diseased  plant  shows  that  its  growth 
has  been  much  retarded  by  the  fungus;  the  leaves  are  curled, 
distorted,  unusually  small,  and  lacking  in  green  color.  Plants 
so  affected  never  recover,  and  are  useless.  Preceding  by 
some  two  or  three  weeks  the  conspicuous  red  rust,  above 
referred  to,  occurs  another  stage  of  the  disease  that  is  often 
overlooked.    This  consists  of  a  thick  growth  of  small  colum- 


Small  Fruits  105 

nar,  glandlike  structures,  chiefly  upon  the  upper  side  of  the 
leaf,  and  present  even  before  the  leaves  unfold.  These 
structures  (pycnia)  become  more  distinct  as  the  leaves 
enlarge. 

The  mycelium  of  the  causal  fungus  when  once  established 
in  the  cane  lives  in  it  from  year  to  year,  spreading  through- 
out the  plant.  Spraying  is,  therefore,  ineffectual.  In  fact 
the  only  successful  way  to  combat  the  rust  is  to  remove 
and  burn  all  affected  plants.  Diseased  plants  are  valueless 
and  are  a  menace  to  the  healthy  plants.  Resistant  varieties, 
such  as  the  Snyder,  should  be  used. 

Late-rust  ^-^  (Kuehneola  albida  (Kiihn.)  Magn.). — As 
the  name  implies,  this  rust  usually  appears  late  in  the  season, 
distinguishing  it  from  orange-rust,  which  is  prevalent  in  the 
spring.  The  spores  are  not  so  abundant  as  those  of  orange- 
rust,  but  occur  in  small,  pale-yellow  or  whitish  spots  scattered 
on  the  under  side  of  the  leaf.  This  disease  has  not  as  yet 
become  sufficiently  prevalent  to  be  of  serious  import,  al- 
though its  increase  at  any  time  under  favorable  climatic 
conditions  may  place  it  among  the  important  plant  enemies. 
It  appears  to  be  limited  to  blackberries,  and  is  known  both 
in  Europe  and  the  eastern  United  States. 

Cane-blight  ^'"^  (Leptosphcpria  coniothyrium  Sacc.  Coniothy- 
rium).  —  First  mentioned  in  literature  in  1899  by  Stewart  and 
Eustace  as  occurring  in  the  Hudson  Valley,  this  disease  seems 
to  be  widespread  and  destructive  upon  both  red  and  black 
raspberries.  Principal  damage  occurs  to  the  fruiting  canes, 
the  foliage  of  which  suddenly  wilts  and  dries.  New  canes 
are  frequently  killed  during  the  first  season's  growth. 

Infection  usually  occurs  through  wounds,  especially 
pruning  wounds  or  those  made  by  insects,  and  progresses 
toward  the  root.  Sometimes  the  disease  remains  upon  one 
side,  while  in  other  cases  it  encircles  the  cane. 

Upon  diseased  canes  the  bark  is  lighter  colored  and  dis- 
figured by  smoke-colored  patches  of  spores  extruded  from 
the  pycnidia  within.  The  pycnidia  appear  as  very  minute 
pustules.      The   wood   is   much   discolored   and   eventually 


106 


Diseases  of  Economic  Plants 


Fig.  52.  —  H.aspberry  cane-blight.    After  Stewart  and  Eustace. 


S7nall  Fruits 


107 


brittle.    This  cane-blight  is  often  erroneously  attributed  to  a 
borer  or  to  drought,  or  winter  injury. 

The  damage  is  often  as  high  as  25 
or  50  per  cent  of  the  crop,  and  the  dis- 
ease is  said  to  be  present  to  some  extent 
in  nearly  all  of  the  raspberry  planta- 
tions in  New  York.  Cuthbert,  Marl- 
boro, Ohio,  Gregg,  Kansas,  and  the 
wild  red  raspberry  are  susceptible.  The 
Columbian  is  more  resistant. 

The  disease  is  disseminated  largely 
by  infected  nursery  stock  or  even  by 
the  soil  adhering  to  the  roots  of  diseased 
plants,  and  is  conveyed  from  plant  to 
plant  by  wind  or  rain,  by  pickers,  or 
by  workmen  while  pruning  and  layer- 
ing, also  by  tools  used  in  cultivation. 
See  soil  diseases,  p.  26.  Since  the  fun- 
gus can  live  on  dead  fragments  of  canes, 
etc.,  upon  the  ground,  these  prove 
fruitful  means  of  propagating  the  pest. 

To  prevent  the  disease,  care  in  the 
selection  of  healthy  plants  is  necessary. 
Plants  should  not  be  set  where  the 
disease  has  prevailed  in  previous  years. 
When  the  fungus  has  gained  access  to 
a  plantation,  all  dead  canes  should  im- 
mediately be  cut  out  and  burned  and 
all  fragments  scrupulously  removed 
from  the  ground.  Spraying  is  of  doubt- 
ful value. 

Spur-blight  ^^^'  ^^^  {Mycosphcerella 
rubina  (Pk.)  Jacz.).  —  On  black  and 
red  raspberry  canes  in  autumn,  sharply  defined,  brown  or 
bluish  black  areas  from  2-10  cm.  long  occur  on  the  bark, 
never  on  the  wood.  In  the  spring  these  spots  bear  numer- 
ous small  pycnidia. 


Fig.  53.  —  Raspberry 
discolored  by  spur- 
blight.  After  Stew- 
art and  Eustace. 


108  Diseases  of  Economic  Plants 

This  disease  has  been  especially  destructive  in  Colorado. 
Three  applications  of  Bordeaux  mixture,  3-2-50,  with  2 
pounds  of  rosin-fish-oil-soap  as  an  adhesive,  applied: 
(1)  when  the  canes  were  8-12  in.  high;  (2)  two  weeks  later; 
(3)  two  weeks  later,  gave  excellent  results  in  Colorado. 

Yellows.  ^'^^  —  Affected  plants  are  stunted,  yellowish,  and 
recall  peach  yellows.  Laterals  are  dwarfed,  leaves  are  small, 
curled  downward  at  the  margins,  and  yellow-mottled. 
Berries  dry  up  without  ripening  or  are  insipid  when  mature. 
Health  and  disease  may  occur  upon  the  same  plant.  The 
cane  itself  and  roots  appear  normal.  The  disease  appears  to 
be  limited  to  raspberries  and  has  been  recorded  in  many 
states  from  Massachusetts  to  California. 

The  cause  and  remedy  are  not  yet  known.  Diseased  plants 
should  be  burned  and  resistant  varieties  planted. 

Gray-mold  (Botrytis) ,  and  Blue-mold  {Penicillmm) .  — 
These  molds  cause  decay  of  fruit  in  transit.  Care  to  avoid 
wounds  and  over-ripeness,  also  prompt  cooling  and  ventila- 
tion, are  necessary. 

Double-blossom  *  ^^^  {Fusarium  riibi  Wint.).  —  Double- 
blossom  occurs  on  dewberry  and,  to  some  extent,  on  the 
high-bush  blackberry.  It  is  most  abundant  on  the  Lucretias, 
but  is  also  a  serious  pest  on  the  Rathbone.  The  disease 
makes  its  appearance  in  the  spring,  just  as  the  leaf  buds  are 
opening,  although  it  can  be  detected  previous  to  that  time 
by  the  enlargement  of  the  diseased  buds. 

Instead  of  the  normal  shoots  and  leaves  a  witches'  broom 
is  produced;  the  entire  bud  l)eing  involved  or  only  a  part, 
according  to  the  attack.  When  the  flower  buds  open,  they 
show  a  great  variety  of  deformities:  sometimes  only  slightly 
distorted;  sometimes  with  increased  number  of  stamens  and 
petals  and  with  enlarged,  thickened  petals  and  sepals.  Even 
those  flowers  which  appear  most  nearly  perfect  have  dis- 
eased ovaries,  and  the  fruits  from  these  brooms  are  always 
worthless. 

Double-blossom  usually  appears  during  the  second  harvest 
*  Prepared  by  M.  T.  Cook. 


Small  Fruits 


109 


and  continues  to  increase  until  the  plants  entirely  succumb. 
Numerous  late  blossoms  appear  during  the  first  season  and 
increase  in  number  from  year  to  year. 

The  disease  is  due  to  a  fungus,  and  the  infection  of  new 
buds  occurs  during  the  blooming  and  fruiting  season.    For 


Fig.  54. 


•The  Dewberry  double-blossom  showing  witches-broom  of 
the  vine.    After  Cook. 


this  reason  it  is  impossible  to  control  the  disease  by  spraying, 
but  it  may  be  held  in  check  by  removing  and  burning  the 
deformed  buds  as  soon  as  they  begin  to  open,  and  can  be 
easily  detected.  If  this  is  done  early  in  the  season  before 
the  leaves  are  large  enough  to  hide  the  diseased  parts,  a 
man  working  alone  can  care  for  plants  at  the  rate  of  400 
per  hour. 


110  Diseases  of  Economic  Plants 

Blue-stem^'''*  (Vertidllium  caulophagus  (Law).  —  Rasp- 
berries and  blackberries  in  the  Pacific  Northwest  are  affected 
by  blue-stem,  the  first  appearance  of  which  was  noted  in 
1904.  The  fruit  dries  up  before  maturity,  the  leaves  become 
discolored  and  wilt.  Less  commonly  the  canes  turn  dark, 
the  first  blue-black,  striped  discoloration  of  the  shoot  occur- 
ring near  the  ground.  Internally  in  stems,  and  even  in 
roots,  reddish  streaks  are  evident  in  the  wood.  Many 
affected  canes  die,  others  merely  show  the  symptoms  men- 
tioned above. 

BLUEBERRY  AND   HUCKLEBERRY 

No  diseases  involving  special  treatment  are  to  be  noted. 
Numerous  parasitic  fungi  are  recorded,  among  them  Exo- 
basidium,  Gibbera,  Guignardia. 

CRANBERRY  i-^-i-« 

To  lessen  storage  decay,  cranberries  should  not  be  picked 
when  wet,  nor  stored  with  admixture  of  infected  material 
likely  to  result  from  deep  "scooping."  They  should  also  be 
well  ventilated. 

Scald,  blast  {Guignardia  vaccinit  Sh.).- — -The  fruits  are 
attacked  as  soon  as  the  blossom  falls,  or  even  the  blossom 
itself  may  be  blighted.  The  affected  l^erry  shi'ivels,  turns 
black,  and  is  covered  with  pycnidia.  From  such  fruits  the 
disease  spreads  to  other  fruits  and  to  the  leaves.  In  some 
bogs  as  much  as  50  per  cent  of  the  crop  is  thus  de- 
stroyed. This  form  of  disease  is  commonly  designated 
as  "blast,"  while  still  another  form  of  it  has  been  termed 
"scald." 

Scald  may  appear  upon  the  berries,  causing  small,  light- 
colored,  softened,  watery  spots.  These  rapidly  increase  in 
circumference,  and  even  envelop  the  whole  fruit.  Sometimes 
the  diseased  portion  shows  more  or  less  distinct  brownish 
zones.  In  other  cases  the  zones  are  lacking,  and  the  whole 
fruit  becomes  very  soft  and  translucent.     Upon  the  leaves 


Small  Fruits 


111 


irregular,  reddish  brown  spots  with  pycnidia  are  more  rarely 
produced. 

Plants,  after  several  years  of  disease,  die,  as  do  cuttings 
during  the  first  or  second  year.  Thrifty  plants  are  much 
more  resistant  than  weak  ones.  Particular  attention  should, 
therefore,  be  given  to  provide  such  irrigation  as  to  best  favor 
the  health  and  vigor  of  the  plants.  Sanding  the  fields  often 
gives  good  results,  doubtless  due  partly  to  removal  of  con- 
tagion by  covering  infective  material.     It  is  also  advisable, 


Fig.  55.  —  Cranberry  scald  and  blast.    After  Shear. 

for  the  same  end,  to  rake  out  and  burn  all  dead  and  infected 
plants  in  the  autumn.  Cuttings  should  be  taken  from  such 
plants  as  show  resistance  to  the  disease. 

In  spraying  experiments  by  Shear,  five  applications  of 
6-6-50  Bordeaux  mixture,  with  4  pounds  of  rosin-fish-oil- 
soap  added  to  increase  adhering  power,  showed  2.36  per 
cent  of  rotten  berries,  while  the  unsprayed  plats  showed 
92.6  per  cent  of  rotten  berries.  The  cost  of  application  was 
$15  to  120  per  acre,  using  200  gallons  of  mixture  at  each 
application. 

Rot  (Acanthorhynchus  vacdnii  Sh.). — An  effect  upon 
the  berry  very  similar  to  that  of  the  scald  fungus  appears 


112  Diseases  of  Economic  Plants 

first  as  small,  light-colored,  soft  spots,  which  soon  destroy 
the  whole  berry.  Later  small,  dark-colored  blotches  show 
under  the  skin,  but  no  pycnidia  appear.  The  disease  is 
found  in  New  Jersey,  West  Virginia,  Mississippi,  Wisconsin, 
and  Nova  Scotia.  In  importance  it  is  the  second  cranberry 
disease. 

The  treatment  suggested  for  scald  is  also  effective  against 
this  rot. 

Anthracnose  {Glomerella  cingulata  var.  vaccinii  Sh.).  — 
This  rot  is  less  injurious  in  New  Jersey  than  scald,  but  is 
more  common  in  Massachusetts  and  New  England. 

The  three  diseases  just  considered  cannot  well  be  dis- 
tinguished except  by  microscopic  examination.  In  some 
cases  the  berry  becomes  soft  and  light-colored,  but  if  the 
fungus  develops  slowly,  the  diseased  portion  is  not  so  soft. 
To  control  them  the  water  supply  should  be  regulated  so  as 
to  avoid  great  fluctuations  during  the  growing  season. 
Too  little  water  is  more  to  be  avoided  than  too  much. 
Vines  dead  from  disease  should  be  pulled  and  burned. 
Bordeaux  mixture,  at  fourteen-day  intervals,  as  suggested 
above,  is  recommended. 

End-rot  ^-"'  ^^"^  (Fusicoccum  putrefadens  Sh.).  —  This  occurs 
in  all  cranberry  sections  of  the  United  States,  starting  at 
either  end  of  the  fruit  and  causing  softening.  Bordeaux 
mixture,  4-3-50,  with  adhesive,  applied  four  tunes,  (1)  before 
blossoming,  (2)  as  soon  as  most  of  the  fruit  is  set,  (3)  ten 
days  later,  (4)  when  fruit  is  three-fourths  grown,  is  effective. 

Hypertrophy  {Exohasidiuni  oxycocci  Rostr.).  —  Hyper- 
trophy is  known  only  in  Massachusetts,  where  in  1906  it 
did  considerable  damage  in  some  bogs. 

In  this  disease  the  buds  in  the  leaf  axils,  which  normally 
remain  dormant,  grow  out  into  short  shoots  bearing  swollen, 
enlarged  leaves  of  pink  or  light-rose  color.  This  character 
has  given  rise  to  the  name  "false  blossoms." 

Wilt  (Sclerotinia  oxycocci  Wor.).  —  As  the  plants  begin  to 
blossom  the  tips  of  green  shoots  wither.  Then  a  thin,  soft, 
white  moldlike  outgrowth  appears  upon  the  stem  and  leaves. 


Small  Fruits  113 

From  here  the  spores  spread  to  the  open  blossoms  and 
infect  the  young  fruit.  No  further  evidence  of  the  disease 
is  seen  until  the  berry  is  nearly  mature,  when  the  affected 
berries  are  found  to  be  full  of  a  cottonlike  growth,  the 
fungous  mycelium.  At  harvest  time  such  berries  show  a 
grayish,  wrinkled  spot,  and  later  the  whole  berry  becomes 
gray,  shriveled,  and  often  spotted  with  dark-brown  masses 
which  break  through  the  skin.  Such  berries  carry  the  disease 
over  winter. 

The  destruction  by  iire  of  all  infected  fruit  will  lessen  the 
evil  in  succeeding  seasons. 

Gall  {Synchytrium  vaccinii  Thomas) .  —  The  cranberry 
gall,  though  not  widely  known,  has  been  serious  in  some  bogs, 
and  on  account  of  its  rapid  spread  may  become  of  much 
import  in  any  bog  to  which  it  gains  entrance.  The  first 
collection  of  the  fungus  in  America  was  by  Halsted  in  New 
Jersey  in  1886. 

It  is  found  upon  the  leaves,  stems,  flowers,  and  fruit  as 
small  (0.8-1  mm.)  red  galls  which  occur  in  such  profusion 
upon  the  affected  part  as  to  cause  marked  distortion. 

The  disease  is  known  to  recur  year  after  year,  resulting 
in  almost  complete  loss  of  the  crop  in  infected  portions  of 
bogs. 

Other  plants  upon  which  this  gall  occurs  are:  Azalea 
{Rhododendron  viscosum  Torr.),  sheep  laurel  (Kalmia  an- 
gustifolia  L.),  white  alder  (Clethra  almfolia  L.),  leather  leaf 
{Cassandra  calyculata  Don.),  huckleberry  {Gaylussacia  res- 
inosa  T.  &  G.),  wintergreen   {Gaidtheria  procumbens  L.). 

Burning  over  the  infested  areas  is  recommended. 

Numerous  other  fungi  have  been  recorded  on  the  cran- 
berry, producing  more  or  less  disease.    See  literature  cited. 

CURRANT  1^" 

Cane-blight  ^-^'  ^'^  {Boiryosphceria  ribis  Gr.  &  D.,  Macro- 
phoma).  — This  affects  both  currants  and  gooseberries  and, 
reported  in  New  York  and  Delaware,  is  probably  widespread. 
A  sudden  wilt  of  the  leaves  on  one  or  more  canes  in  a  bush 


114  Diseases  of  Economic  Plants 

is  the  first  symptom  of  disease.  The  entire  bush  may  suc- 
cumb, but  not  usually  during  the  first  season.  Upon  splitting 
the  stems  a  discoloration  of  the  bark  and  wood  near  the  base 
is  noticed.    No  effective  treatment  is  known. 

Mycosphaerella  leaf-spot  ^^°-  ^^^  (Mycosphcerella  grossularice 
(Fr.)  Lind.,  Septoria).  —  The  spots  on  the  leaf  are  small 
(3  mm.),  circular,   brown-bordered,   with  blanched  centers 


Fig.  56.  —  Currant  leaf-spot.    After  Stewart  and  Eustace. 

which  bear  numerous,  minute,  black  pycnidia.  Heavy 
infection  causes  defoliation.  Both  currants  and  gooseberries 
are  affected.    Treatment  is  as  for  the  following  disease. 

Angular  leaf-spot  ^^°  {Cercospora  angulata  Wint.).  —  This 
term  is  applied  to  a  pecuHar  spotting  of  the  leaves  of  both 
currants  and  gooseberries.  It  is  likely  to  occur  wherever 
these  plants  are  grown.  The  spot  is  of  rather  characteristic 
appearance,  irregular  or  angular  in  outline,  generally  about 
3  mm.  in  diameter.    In  the  center  of  the  brown  or  gray,  dis- 


Small  Fruits  115 

colored  area,  hyphae  may  be  seen.  Serious  defoliation  often 
results.  Bordeaux  mixture  should  be  used :  five  applications 
at  ten-  to  fourteen-day  intervals,  beginning  as  soon  as  the 
leaves  open. 

Anthracnose  ^^-  (Pseudopeziza  ribis  Kleb.,  Gloeosporium) .  — 
The  leaves,  fruit  stalks,  berries,  and  canes  are  affected. 
Usually  the  disease  is  not  present  to  great  extent,  but  a  few 
serious  outbreaks  have  occurred,  notably  in  central  New 
York,  in  the  Hudson  River  region,  and  in  Oregon.     It  has 


Fig.  57.  —  Currant  anthracnose.    Alter  Stewart  and  Eustace. 

also  been  noted  in  Ohio,  Iowa,  New  Jersey,  and  is  probably 
often  present  to  a  slight  extent  in  other  states.  It  is  less 
common  on  gooseberries. 

In  a  severe  outbreak  the  leaves  first  become  covered  with 
small,  dark-brown  spots,  change  to  yellow,  and  soon  fall. 
By  the  time  the  fruit  has  ripened,  practically  all  of  the 
leaves  may  be  lost.  Upon  the  leaf  stalks,  also  upon  the  fruit, 
stems,  and  canes,  the  disease  appears  as  little,  black,  sunken 
spots.  On  the  berries  the  spots  are  circular  and  black,  much 
resembling  fly  specks.  The  causal  fungus  probably  winters 
upon  the  canes,  ready  to  initiate  the  spring  infection. 


116 


Diseases  of  Economic  Plants 


Anthracnose  can  readily  be  distinguished  from  the  leaf 
spots  mentioned  above  by  the  fact  that  the  spots  produced 
in  anthracnose  are  very  much  smaller,  less  angular,  and 
lack  in  every  way  the  distinguishing  characters  of  the  other 
leaf  spots. 

No  conclusive  evidence  as  to  the  best  treatment  is  at  hand. 
The  best  recommendation  is  probably  that  of  the  Geneva 


Fig.  58.  —  Anthracnose  of  white  currants.    After  Clinton. 


Experiment  Station:  "Spray  thoroughly  with  Bordeaux 
mixture,  commencing  before  the  leaves  appear.  Make  the 
second  treatment  as  the  leaves  are  unfolding  and  thereafter 
at  intervals  of  ten  to  fourteen  days  until  the  fruit  is  two-thirds 
grown.  In  wet  seasons  make  one  or  two  applications  after 
the  fruit  is  gathered.  When  worms  appear,  add  Paris  green 
or  green  arsenoid  to  the  Bordeaux." 

European  rust  {Cronartium  ribicola  F,  v.  Wal.).  —  Orange- 


Small  Fruits  117 

colored  powder  appears  upon  the  lower  surface  of  the  leaves 
of  currants  and  gooseberries  accompanied  by  but  slight  dam- 
age. The  spring  stage  occurs  upon  trunks  and  branches  of 
the  white  pine,  and  is  there  very  destructive.  For  history, 
distribution,  and  general  discussion,  see  pine. 

Minor  diseases 

Powdery-mildew,  see  gooseberry;  Root-rots  due  to  Armil- 
laria,  see  apple,  to  Fomes  ribis  (Schw.)  Fr.,  see  gooseberry; 
Silver-leaf,  see  plum ;  Cluster-cup-rust,  see  gooseberry. 

DEWBERRY.    See  blackberry. 

GOOSEBERRY  i^" 

Powdery-mildew  ^^^  (Sphcerotheca  mors-uvce  (Schw.)  B.  & 
C). — This  disease  appears  to  be  of  American  origin, 
whence  it  invaded  Europe,  appearing  first  in  Russia  in  1890 
and  in  Ireland  about  1900.  It  is  now  general  in  Europe 
where  it  is  much  more  destructive  than  here.  The  mildewed 
appearance  of  the  leaves,  stems,  and  fruit,  all  of  which  appear 
whitened  as  though  dusted  with  flour,  is  characteristic. 
Close  inspection  shows  each  blotch  to  consist  of  cobwebby 
threads  densely  matted  in  the  central  portions  of  the 
spot.  Later  these  blotches  turn  brown,  blend  irregularly 
into  fewer  spots,  and  form  large  diseased  areas.  As  the 
spot  ages,  its  threads  weave  together  into  a  thick  brown- 
ish felt. 

The  young  leaves  and  growing  parts  are  robbed  of  nourish- 
ment, and  thus  their  growth  is  checked,  resulting  in  serious 
injury.  The  berries,  if  subjected  to  one-sided  attack,  become 
deformed  and  curved,  owing  to  the  retarded  growth  of  the 
diseased  side.  They  often  crack  open  and  decay.  Diseased 
leaves  turn  brown.  Toward  the  completion  of  the  season's 
growth  small,  nearly  microscopic,  Ijlack  perithecia  are  pro- 
duced in  the  centers  of  the  diseased  spots. 

The  damage  caused  by  powdery-mildew  is  excessive  and 
presents  the  most  serious  obstacle  to  the  successful  culture 


1 18  Diseases  of  Economic  Plants 

of  the  gooseberry.  It  has  quite  prohibited  the  cultivation 
of  the  finer  sorts  of  Enghsh  gooseberries  in  America  and 
is  a  grave  menace  to  the  culture  of  gooseberries  in  Europe. 
Its  destructiveness  is  due  not  alone  to  injury  to  the 
fohage,  bush,  and  to  the  fruit  yield,  but  also  to  lack  in 


Fig.  59.  —  Stages  at  which  spraying  should  be  given  for  mildew. 
After  Close. 

salability,  owing  to  the  unsightliness  of  the  partially  diseased 
fruits. 

This  powdery-mildew  has  been  very  successfully  combated 
by  use  of  potassium  sulfid,  1  ounce  to  2  gallons  of  water,  or 
lime-sulfur,  spraying  five  or  six  times.  This  treatment  has 
been  known  to  reduce  the  percentage  of  mildewed  fruits 
from  sixty-three  on  the  untreated  Ijushes  to  eighteen  on  the 
treated  bushes.    The  proper  time  to  spray  is  indicated  in  the 


Small  Fruits  119 

accompanying  figure.  Treatment  should  be  begun  at  the 
condition  shown  in  the  left-hand  figure,  and  continued  at 
intervals  of  ten  days  or  two  weeks  until  the  requisite  number 
of  applications  have  been  made.  Spraying  begun  when  the 
bushes  are  in  the  condition  shown  in  the  left  figure  gives 
decidedly  better  results  than  when  the  spraying  is  delayed 
until  the  condition  shown  in  the  other  two  figures. 

Cluster-cup  (Puccinia  pringsheimiana  Kleb.,  jEcidium).  — 
Occasionally  reddish,  swollen,  or  thickened  spots  are  noticed 
over  the  leaves  and  sometimes  upon  the  fruit  of  currants  and 
gooseberries.  Close  examination  shows  each  spot  to  consist 
of  a  cluster  of  minute  cups  embedded  in  the  tissue  of  the 
leaf,  whence  the  name  "cluster-cup."  With  a  lens  each  cup 
is  seen  to  consist  of  a  fringed  rim  extending  above  the  surface 
of  the  leaf,  and  to  be  filled  with  very  small,  red  spores. 

The  winter  condition  is  found  upon  quite  different  plants; 
namely,  various  common  sedges  (Carex)  upon  the  leaves  of 
which  it  constitutes  a  genuine  rust. 

The  damage  is  not  serious,  and  no  experiments  on  a  large 
scale,  in  prevention,  have  been  undertaken.  If  it  should 
prove  destructive,  thorough  eradication  of  the  sedges  in  the 
neighborhood,  particularly  any  that  are  rusted  in  autumn, 
would  be  deemed  necessary. 

Root-rots.  —  Root-rots  upon  both  the  gooseberry  and 
currant  have  been  reported  from  various  states. 

The  plants  die  slowly.  When  dead  and  living  canes  are 
found  in  the  same  hill,  the  living  canes  are  somewhat  dwarfed. 
The  fungi  apparently  spread  through  the  soil,  and  the 
infested  area  enlarges  year  by  year. 

Little  can  be  suggested  in  the  way  of  treatment.  It  is, 
however,  best  to  pull  up  and  burn  affected  plants,  and  it 
is  inadvisable  to  place  susceptible  crops  upon  soil  which  is 
known  to  be  infested.  These  rots  have  been  attributed  in 
part  to  Arniillaria,  see  apple. 

Anthracnose  and  Leaf-spots  are  much  as  on  the  currant; 
the  Blister-rust  is  less  common  than  on  the  currant. 


120 


Diseases  of  Economic  Plants 


r^ 


^73 


GRAPE 

The  high  acreage  value  of  the  crop,  the  long  life  of  the 
individual  vine,  the  numerous,  serious  diseases  to  which  the 
vine  is  subject,  and  the  fact  that  it  was  one 
of  the  crops  first  to  be  commercially  sprayed, 
renders  the  grape  of  especial  interest  to  the 
plant  pathologist. 
■Black-rot     ^^^~^^^     (Guignardia    hidwellii 

O^  (Ell.)  V.  &  R.,  Phyllosticta).  — This  wide- 
g  spread  and  exceedingly  destructive  disease, 
■:=  the  first  record  of  which  dates  back  to  1861, 
I  ^-  has  been  responsible  for  the  abandonment 
of  grape  culture  in  many  sections  of  the 
country.      It    is    of    general    distribution 

»  y   5  -a    throughout    the    United    States,    also    in 

\^^^^^^  "Z  i  Europe  and  Asia.  In  1906  in  Michigan  the 
loss  from  black-rot  was  estimated  at  30  to 
40  per  cent  of  the  crop;  in  Ohio  in  1905  at 
30  per  cent  of  the  crop  worth  $95,000.  In 
many  sections  the  loss  is  practically  total 
unless  measures  are  taken  to  check  its 
ravages. 

In  its  most  familiar  form  the  disease  con- 
sists of  spotting  and  decay  of  the  fruit. 
Black  or  brown  spots,  one  or  more  in  num- 
ber, at  first  infinitesimal  in  size,  appear 
upon  the  berry.  The  spots  enlarge  with 
great  rapidity,  one  spot  in  a  few  days  en- 
compassing the  whole  berry  and  changing 
it  into  a  black  mass.    As  the  rot  progresses 

J^^^^^i  d        the  skin  remains  intact,  and  soon  the  berry 

*^i^BPI's&,1  ^  begins  to  shrink  and  shrivel  until  it  is 
eventually  merely  a  dry,  hard,  wrinkled, 
mummified  fruit.    The  rapidity  with  which 

this  change  takes  place  is  shown  in  the  accompanying  figure. 

Many  of  the  berries  so  mummified  fall  to  the  ground,  others 

remain  upon  the  vine. 


Small  Fruits 


121 


Upon  the  leaves  the  disease  appears  considerably  earlier 
than  upon  the  fruits.  Here  it  produces  tan-colored  spots 
about  3-8  mm.  in  diameter,  many  or  few  according  to  the 
severity  of  the  infection.  In  or  near  the  centers  of  the  older 
spots,  upon  the  upper  surface  of  the  leaves,  are  seen  the 
nearly  microscopic  pycnidia  which  are  often  arranged  in 
concentric  circles. 

On  the  young  shoots  the  spots  are  somewhat  more  reddish 
and  are  often  cracked  longitudinally, 
but  otherwise  they  are  as  upon  the 
leaves. 

This  rot  is  much  more  prevalent 
in  warm,  humid  weather  than  in 
dry  times,  and  a  few  days  of  muggy 
weather  may  so  favor  the  growth 
of  the  causal  fungus  as  to  develop 
an  epidemic,  which  may  in  turn  be 
checked  by  a  dry  spell.  Often  the 
disease  appears  in  distinct  waves 
during  the  season,  each  wave  cor- 
responding to  a  climatic  condition 
favorable  to  infection  and  usually 
lagging  behind  such  favorable  con- 
dition a  period  of  8  to  14  days,  the 
time  necessary  after  infection  for 
the  disease  to  become  conspicuous 
enough  to  attract  the  attention  of 
the  vineyardist. 

While    the     Scuppernong     occa- 
sionally shows  a  few  spots  upon  leaf  or  berry  and  the  blossom 
is  sometimes  affected,  this  variety  is  practically  immune. 

To  prevent  the  inroads  of  black-rot,  thorough,  clean  cul- 
ture should  be  practiced.  All  mummified  fruit  should  be 
burned  to  avoid  infection.  Keep  the  ground  free  from 
sprouts  and  all  other  growths  and  i:)ermit  no  weeds  or  grass. 
Cover  crops  are  beneficial.  Plow  early  so  as  to  cover  all  re- 
maining leaves  and  berries  that  Ijear  the  hibernating  fungus. 


-  Grape  black- 
Original. 


122 


Diseases  of  Economic  Plants 


Use  a  dormant  spray  to  clean  the  bark,  trellis,  etc.  The 
utility  of  this  first  spraying  may  vary  with  climatic  condi- 
tions and  latitude.  Use  foliage  sprays  of  5-5-50  Bordeaux 
mixture  throughout  the  sunnner.  Five  or  sLx  applications 
are  usually  necessary.  The  first  should  be  made  when  the 
shoots  are  20-30  cm.  long,  the  others  at  intervals  of  ten  to 
fourteen  days.  After  the  first  two  applications  the  spray 
must  reach  the  clusters  to  be  effective.  Spraying  each 
season  is  necessary;  neglect  one  season  brings  large  increase 
in  the  rot  the  following  season. 

The  following  table  shows  the  benefits  of  careful,  thorough 
spraying. 

Result  of  Black-Rot  Experiments  in  1908 


Plat 
No. 

Treatment 

Net 
Weight 

Har- 
vested 

Weight 
Firsts 

Weight 
Wine 

Weight 
Rotten 

Firsts 
Per 
Cent 

Wine 
Per 
Ce.nt 

Rotten 
Per 
Cent 

1 

Bordeaux 
4-4-50,        6 

lb. 

lb. 

lb. 

//». 

applications 

8081 

7252 

742 

9) 

89 . 7 

9.2 

1.1 

2 

Bordeaux 
5-5-50,        4 

applications 

7872 

74(;i 

31)-) 

10  1 

91.. S 

3 . 9 

1.3 

3 

Bordeaux 
5-5-50,        6 

applications 

'.)ir)7 

S72  J 

31):; 

125 

95 . 3 

3 . 3 

14 

' 

Sprayed  ac- 
cording to 
weather  con 

ditions 

7997 

7588 

33S 

71 

91.9 

4    2 

0.9 

5 

Cultivated  but 

not  sprayed 

3175 

2232 

451 

4'.)2 

70.3 

14.2 

15.5 

(', 

Neither  culti- 

vated nor 

sprayed  ... 

3331 

2109 

594 

571 

65.1 

17.8 

17.1 

Powdery-mildew  ^^"^^  *°'^  (Undnula  necator  (Schw.)  Burr., 
Oidium) .  —  This  mildew  was  first  noted  in  Europe  about 
1845,  near  London,  and  shortly  after  in  Belgium  and  France, 
and  is  said  to  have  reached  every  grape-growing  country  of 
Europe  before  1851.  It  increased  in  severity  until  1854  when 
it  began  to  he  held  in  check  by  sulfur  applications.  It  is 
known  in  all  parts  of  the  United  States,  but  is  less  destructive 
here  than  abroad,  though  in  certain  localities  in  New  York, 


Small  Fruits 


123 


Oregon,  and  California,  it  is  regarded  as  the  most  important 
grape  disease. 

Powdery-mildew  attacks  all  parts  of  the  plant  except 
the  roots,  showing  first  upon  both  the  upper  and  lower 
surface  of  young  leaves  as  whitish  circular  spots,  which  ap- 
pear somewhat  as  though  dusted  with  flour.  These  spots 
enlarge,  coalesce,  and  may  cover  the  whole  leaf.  The  af- 
fected leaf  is  retarded  in  growth  and  becomes  distorted. 
Mildewed  blossoms  fail  to  set  their  fruit,  and  fruit  that 


Fig.   62.  —  Black-rot  as  it  shows  on  the  leaves. 
After  Anderson. 


is  mildewed  soon  ceases  growth  and  falls,  or  develops  ir- 
regularly and  fails  to  ripen. 

The  mildew  fungus  is  strictly  superficial  and  may  be 
rubbed  off,  leaving  a  discolored  spot.  In  late  stages  perithecia 
may  be  recognized  as  very  small  black  bodies,  about  0.1- 
0.12  mm.  in  diameter,  lying  within  the  diseased  areas.  The 
disease  develops  in  most  destructive  form  in  shaded,  damp, 
poorly  ventilated  situations.  Rain  and  fogs  favor  it,  while 
very  dry  weather  inhibits  it.  The  American  vines  are  less 
susceptible  than  the  European  varieties. 


124 


Diseases  of  Economic  Plants 


Ventilation  and  removal  of  shading  trees  are  beneficial. 
Close  planting  should  be  avoided  in  order  to  allow  quick 
drying,  trelhses  should  run  in  such  direction  as  to  allow  free 
access  of  sun.     But  these  means  are  only  palliative. 

To  control  the  mildew  in  dry  climates  employ  flowers  of 
sulfur.  The  sulfur,  when  the  temperature  is  above  24°  C. 
(75°  F.),  passes  into  the  air,  and  its  fumes,  coming  in  contact 


Fig.  63. 


Black-rot  spots  fiilargccl  to  show  the  pycnidia. 
After  Anderson. 


with  the  fungus,  kill  it.  Below  the  temperature  at  which 
sulfur  is  effective  the  fungus  will  make  but  Httle  progress. 
When  the  air,  shade  temperature,  is  from  32°  to  35°  C.  (90° 
to  95°  F.),  the  killing  effect  of  the  sulfur  may  be  seen  within 
24  hours;  if  above  38°  C.  (100°  F.),  one  or  two  days  are  suf- 
ficient to  rid  the  vineyard  of  the  disease.  The  sulfur  must 
be  distributed  to  every  part  of  the  vine.  Sulfur  upon  the 
ground  is  of  no  use.  The  vines  should  be  dusted  from  one  to 
seven  times,  according  to  conditions,  susceptibility,  climate, 
etc.    The  first  sulfuring  should  be  done  when  the  blossoms 


Small  Fruits  125 

begin  to  open;  a  second  application  should  be  made  before 
the  first  sign  of  the  mildew,  and  other  applications  should 
follow  as  need  indicates.  It  is  necessary  to  resulfur  if  from 
one  to  two  days  at  32°  to  35°  C.  (90°  to  95°  F.)  or  four  to  five 
days  at  29°  to  32°  C.  (85°  to  90°  F.)  do  not  intervene  before 
the  sulfur  is  removed  by  rain.  If  the  disease  was  destructive 
the  previous  year,  it  is  well  to  make  application  even  earlier 
than  indicated  above,  i.  e.,  when  the  shoots  are  about  15- 
20  cm.  long. 

After  the  grapes  commence  to  ripen  they  are  comparatively 
safe  from  mildew,  but  for  the  future  good  of  the  vine  the 
leaves  should  be  protected  by  further  sulfuring  if  need  be. 
Young  vines  should  similarly  be  protected.  To  properly 
apply,  use  good  dusting  machines  which  give  an  even  flow 
of  sulfur  and  are  easy  of  operation. 

In  climates  where  sulfur  cannot  be  used  to  advantage 
reliance  must  be  placed  upon  Bordeaux  mixture  or  hme- 
sulfur  applied  as  for  the  black-rot. 

.Downy-mildew  ^^^'  ^^-'  ^"^^  (Plasmopara  viticola  (B.  &  C.) 
Berl.  &  de  Toni) .  —  Downy-mildew  produces  a  more  or 
less  distinctly  visible  downy  or  velvety  growth  upon  the 
affected  surface,  caused  by  myriads  of  spore-bearing  stalks 
that  rise  from  the  diseased  surface.  If  these  stalks  are 
close  together,  the  appearance  is  thoroughly  characteristic 
and  the  diagnosis  clear.  As  the  spores  mature  the  spots 
assume  a  gray  or  frosted  appearance. 

The  European  grapes  are  more  susceptible  to  this  mildew 
than  the  American  varieties.  All  the  green  parts  of  the  plant 
are  affected.  Upon  the  lower  side  of  the  leaf  the  disease 
may  be  recognized  by  the  description  given  above.  The 
upper  surface  of  the  leaf  over  a  diseased  spot  becomes  pale, 
yellowish,  and  finally  turns  brown  and  dies.  The  area  so 
affected  is  definitely  bordered  and  does  not  necessarily 
cause  the  death  of  the  whole  leaf,  though  it  may  do  so. 

Upon  shoots  the  same  characteristic  appearance  is  noted 
as  upon  the  lower  surfaces  of  the  leaves.  Sometimes  the 
death  of  the  affected  twig  or  even  of  the  whole  vine  results; 


126 


Diseases  of  Economic  Plants 


Fig.  64.  —  Downy-mildew  as  seen  from  the  lower  surface  of  the  leaf.  After  Heald. 


Small  Fruits 


127 


Immature  berries  which  are  affected  cease  growing  and  de- 
velop the  same  coating  noted  upon  the  leaves,  giving  rise  to 
the  name  ''gray-rot."  If  the  berries  are  more  mature  when 
attacked,  they  turn  brown,  thus  calling  forth  the  name 
"brown-rot."     The  berry  in   dying  shrivels  and  becomes 


Fig.  65.  —  Youiu 


Niagara  clusters  attacked  by   downy-mildew. 
After  Lodeman. 


wrinkled,  but  does  not  become  hard  and  dry,  as  in  the  case 
of  the  black-rot.  The  disease  is  usually  more  troublesome 
in  the  early  part  of  the  season  than  in  autumn.  Effective 
management  requires  early  Bordeaux  spraying,  just  before 
the  blossoms  open,  and  often  it  will  be  found  advantageous 
to  protect  the  leaves  by  two  to  five  additional  sprayings  at 
intervals  of  about  two  weeks.     This  disease  was  noted  in 


128 


Diseases  of  Economic  Plants 


America  as  early  as  1834,  and  was  carried  to  Europe  about 
1878.  It  is  now  general  both  in  Europe  and  the  United 
States. 

Anthracnose  ^^"'  ^"^^  (Gloeosporium  ampelophagumSsiCC.).  — 
This  anthracnose,  probably  introduced  into  America  from 
Europe  prior  to  1880,  is  now  widely  distributed  throughout 


Fig.  66.  —  Anthracnose  on  the  fruit.    After  Paddock. 

grape-growing  sections  and  is  the  fourth  disease  in  impor- 
tance. While  not  usually  so  destructive  as  black-rot  or 
brown-rot,  it  sometimes  increases  to  such  an  extent  as  to  do 
great  damage,  even  causing  in  some  instances  the  loss  of  all 
the  berries  upon  a  vine  as  well  as  much  injury  to  the  canes. 
During  damp,  warm  weather  it  develops  rapidly,  affecting 
some  varieties  more  than  others.  The  Champion  and 
Moore's  Diamond  may  be  mentioned  as  especially  sus- 
ceptible, while  the  Concord  is  resistant. 


Small  Fruits  129 

Upon  the  canes  the  anthracnose  is  first  seen  as  small,  dark 
brown  or  black  spots,  which  soon  become  sunken  in  the 
centers.  The  spots  usually  enlarge  rapidly  lengthwise  of  the 
stem,  though  they  may  sometimes  girdle  it.  Girdling  is 
particularly  common  upon  stem  clusters,  where  it  is  always 
fatal.  The  centers  of  the  older  spots  are  ashen  in  color,  the 
edges  dark,  and  the  cankerlike  spot  extends  from  the  bark 
deep  into  the  wood,  rendering  the  shoot  weak  and  brittle. 

Upon  the  fruit,  spots  3-5  mm.  in  diameter  are  produced 
similar  to  those  upon  the  canes,  except  that  the  center  does 
not  always  become  ashen.  Here,  too,  a  band  of  red  often 
surrounds  the  diseased  part.  The  parts  of  the  berry  adja- 
cent to  the  diseased  spot  remain  green  and  develop  normally, 
which,  associated  with  the  red  border,  results  in  the  peculiar 
appearance  which  has  led  this  disease  to  bear  the  name 
"bird's-eye  disease." 

If  the  berry  is  attacked  while  young,  it  may  either  out- 
grow the  disease  or  succumb  to  it.  Several  spots  upon  one 
berry  destroy  its  value,  and  spots  upon  one  side  may  cause 
distortion,  cracking,  and  exposure  of  the  seeds. 

Upon  the  leaves  the  dead  spots  are  usually  bordered  by  a 
fine  black  line,  and  as  the  leaf  enlarges  the  dead  tissue  of  the 
spot  may  rupture  irregularly. 

Badly  anthracnosed  canes  must  be  cut  out  and  burned, 
and  a  dormant  spray  applied,  followed  by  protective  sprays 
as  for  black-rot. 

Necrosis,  Dead-arm  ^^^'  ^'^^  {Cryptosporella  viticola  (Red.) 
Sh.,  Fusicoccimi) .  —  This  disease  has  been  noted  in  New 
York,  Ohio,  Georgia,  and  Indiana.  It  is  said  to  cause  loss  of 
from  1  to  5  per  cent  annually  in  New  York.  The  Concord, 
Niagara,  Moore's  Early,  Agawams,  Pocklingtons,  Wordens. 
Lindleys,  Catawbas,  Isabellas,  and  Scuppernong  are  sus- 
ceptible. 

Necrosis  may  be  recognized  in  the  field  by  the  following 
characters:  A  trimmed  and  tied  vine  that  has  failed  to 
put  out  shoots;  one  that  has  sent  forth  shoots,  the  latter 
dying  after  a  few  weeks;  vines  on  which  all  or  part  of  the 


130 


Diseases  of  Economic  Plants 


shoots  and  leaves  exhibit  a  dwarfing,  with  leaves  small  and 
often  crimped  about  the  margin ;  leaves  of  nearly  normal  size 
but  blanched;  apparently  healthy  vines  with  leaves  and  fruit 
shriveling  and  dying  in  the  summer;  fleshy  or  corky  longi- 
tudinal excrescences  on  the  stem,  which  in  the  autumn  dry 
down  and  become  reddish  brown  and  the  following  spring 
slough  off;  the  presence  of  minute  black  pustules  on  a  dead 

spur,  bark,  or  wood  under 
the  bark;  small  reddish  brown 
spots  3-4  mm.  long  on  the 
green  shoots. 

The  disease  is  conveyed  to 
new  tissue  by  spores  from 
the  pycnidia,  also  probably 
by  pruning  tools.  It  may 
also  enter  the  older  parts 
through  wounds.  Cuttings 
bearing  the  fungus  probably 
spread  the  disease. 

Spraying  shoots  with  Bor- 
deaux mixture  when  from 
73^-15  cm.  long  will  reduce 
infection.  Diseased  vines  should  be  pulled  and  burned,  or 
if  the  root  crown  be  still  sound,  they  may  be  cut  back  to 
near  the  ground,  when  the  renewal  will  be  healthy.  In  the 
spring  and  summer  it  is  well  to  mark  sick  vines  for  future 
eradication.  Cut  off  the  diseased  parts,  using  tools  not 
used  in  ordinary  pruning. 

Root-rot  ^^^  (various  fungi) .  — •  This  rot  attacks  a  few 
roots  at  first,  but  eventually  reaches  all,  and  results  in  death 
of  the  vine.  It  is  very  destructive  in  Europe  and  has  been 
noted  in  several  places  in  the  United  States. 

The  top  growths  of  affected  vines  show  symptoms  first; 
then  follows  one  division  after  another  until  a  large  vine 
is  reduced  to  the  size  of  a  bushel  basket,  though  numer- 
ous lateral  canes  may  arise,  especially  near  the  base  of  the 
plant.    The  leaf  color  usually  remains  normal  v/ith  no  dead 


p.  ^x-. 

f 

^^ 

^^  ^S<4 

ll' 

^^m 

W-' 

9^^ 

fe^ 

^r 

ki 

^^ 

1^../ 

Fig.  67.  —  Necrosis  of  the  vine. 
After  Reddick. 


Small  Fruits 


tissue,  though  the  leaves  sometimes  turn 
yellow,  and  many  of  them  are  reduced  in 
size.  After  the  vine  dies  the  leaves  still  re- 
main attached  to  the  canes.  The  best  treat- 
ment is  to  remove  and  burn  the  affected 
stock,  thoroughly  stir,  air,  and  dry  the  adja- 
cent soil.  For  further  discussion  of  root-rot, 
see  p.  370. 

Several  diseases,  the  causes  of  which  are 
not  known,  do  serious  injury  to  the  grape. 
They  may  be  briefly  described  as  follows: 
California  vine-disease.^^''  Since  1884 
many  vineyards  in  California  have  been 
destroyed  by  this  disease.  In  the  first  sea- 
son small,  yellow  spots  appear  between  the 
veins.  These  enlarge  and  unite  to  form 
stripes,  leaving  only  a  narrow  band  of  green 
tissue  along  the  veins.  Leaves  fall  prema- 
turely and  the  canes  turn  black  and  die. 
The  following  season  there  is  reduced  growth 
of  canes.  By  the  third  or  fourth  season  the 
vines  usually  die.  Cuttings  should  not  be 
made  from  diseased  vines.  An  unnamed 
disease  of  somewhat  similar  character  has 
been  described  in  New  York.^"*^  Brunissure. 
Irregular  brown  spots  appear  on  the  upper 
surfaces  of  the  leaves  and  the  epidermis 
falls  away,  exposing  the  underlying  tissue. 
Later  the  browning  extends  through  to  the 
lower  leaf  surface.  Black  zones  often  ap- 
pear in  the  wood.  Shelling  consists  in  the 
grapes  falling  from  their  stems  Ijefore  ma- 
turity. Diseased  berries  are  matted,  thick- 
skinned,  and  show  a  brown  zone  l)eneath 
the  skin.  Though  the  cause  of  shelling  is 
unknown,  it  is  more  common  on  weak 
vines.     Good  cultural  conditions  lessen  it. 


Fig.  68.  —  Grape 
necrosis  as  it 
appears  on  the 
canes.  After 
Reddick. 


132  Diseases  of  Economic  Plants 

Blue-mold  rot  ^^^  {Penidllium).  —  Grapes  should  be  handled 
to  avoid  wounds,  carefully  packed,  and  shipped  or  stored  at 
as  nearly  0°  C.  (32°  F.)  as  possible  to  prevent  large  loss  due 
to  blue-mold. 

Minor  diseases 

Crown-gall  ^^^  (see  apple)  is  common  on  the  grape,  with 
a  wide  difference  in  susceptibility  between  varieties;  Bitter- 
rot  comes  late  in  the  season  on  the  fruit  when  nearly  ripe,  see 
apple;  White-rot  (Charrina) ,  Scab  {Cladosporium  viticolum 
Ces.),  Gray-rot  {Sclerotinia  fuckelianxi  (De  Bary)  Fcl.),  and 
Cercospora  leaf-spot  are  usually  of  but  little  injury. 

HUCKLEBERRY.    See  blueberry. 

RASPBERRY.    See  blackberry. 

STRAWBERRY 

Leaf-spot  ^•'^'  ^''^  {Mycosphcerella  fragarioe  (Tul.)  Lin,, 
Ramularia) .  —  The  most  conspicuous  disease  of  the  straw- 
berry, one  nearly  always  present  to  some  extent  on  both  wild 
and  cultivated  varieties  in  Europe  and  America,  is  recognized 
by  the  presence  of  small,  4-6  mm.,  purple  or  red-bordered 
spots  upon  the  leaves,  the  older  spots  bearing  white  or  ashen 
centers.  Late  in  the  development  of  the  spots  the  hyphse  of 
the  causal  fungus  are  barely  visible  with  a  good  hand  lens. 
The  spots,  when  numerous,  may  coalesce,  forming  large, 
irregular  blotches.  The  disease  is  also  very  injurious  in  its 
attacks  upon  the  fruit  stems,  resulting  in  diminution  of  food 
supply  to  the  fruit  and  its  improper  development. 

It  attacks  all  varieties,  precluding  the  use  of  especially 
susceptible  varieties  in  some  localities,  often  killing  the 
plants,  and  in  any  event  lessening  their  vigor  and  produc- 
tiveness. In  some  localities  entire  plantings  have  been  de- 
stroyed. One  grower  reports  a  loss  of  $1500  on  a  six-acre 
field  in  one  season. 


Small  Fruits 


133 


Moisture  and  heat  favor  the  development  of  the  fungus, 
while  moisture  upon  the  leaves  is  essential  to  infection. 
Weather  favorable  to  infection  followed  by  hot,  dry  days 
may  be  attended  by  great  injury.  Heavy,  wet,  undrained 
soil  also  conduces  to  disease. 


Fig.  69.  — ■  Strawberry  leaf-spot.     After  Freeman. 


Frequent  change  of  beds;  also  cutting,  gathering,  and 
burning  or  burying  of  tops  in  place  after  harvest,  and  the  use 
of  Bordeaux  mixture  after  the  removal  of  the  diseased  leaves 
will  lessen  the  infection  of  the  next  year. 

Hume  in  Florida  found  that  l)y  means  of  three  early  spray- 
ings of  4-4-40  Bordeaux  mixture,  the  disease  was  so  checked 
that  "it  was  a  difficult  matter  to  find  a  leaf  at  all  diseased  in 
the  whole  patch."  Later,  when  tlie  disease  began  to  make 
headway  again,  another  spraying  controlled  it. 


134  Diseases  of  Economic  Plants 

Powdery-mildew  (Sphoerotheca  humuli  (DC.)  Burr.). — 
This  mildew  may  he  recognized  by  the  characters  usually 
pertaining  to  the  powdery-mildews.    (See  grape.) 

Upon  the  strawberry  it  induces  curled,  in-rolled  leaves, 
and  the  white  mycelium  is  found  upon  their  lower  surfaces. 

The  disease  is  not  usually  troublesome. 

Botrytis-rot  ^^^  {Botrytis  sp.).  —  This  rot,  though  prevalent 
in  the  fiekl,  occasions  serious  loss  only  on  l^erries  which  are 
shipped  over  long  hauls.  The  rotten  spot  is  dry,  tan-colored, 
and  finally  covered  with  downy  spore  clusters.  Careful 
sorting  to  avoid  shipping  of  infected  berries  is  necessary. 
Infected  fruit  that  is  sorted  out  should  be  buried  with  lime. 

Leak  ^''^  {Rhizopus  nigricans  Ehr.).  —  Berries  often  decay 
in  shipment,  the  juices  leaking  out  from  the  bottoms  of  the 
boxes.  The  berries  sink  to  a  feltlike  layer  covered  by  mold 
and  its  black  sporangia.  This  rot  causes  millions  of  dollars 
loss  annually.  Only  sound  berries  should  be  offered  for  ship- 
ment. 

Miyior  diseases 

Leaf-blight  ^-'^  due  to  Aposphseria;  Leaf-spot  due  to 
Ascochyta;  Fruit  rots  due  to  Sphgeronemella,^^^  Patellina,^" 
and  occasionally  to  the  black-rot  fungus,  Physalospora/^^ 
do  some  injury. 


TROPICAL  FRUITS 
AVOCADO 

Anthracnose  {Colletotrichum  gloeosporioides  Penz.). — At- 
tack upon  the  leaves  eventually  causes  defoliation.  Early 
infection  of  the  fruit  results  in  its  complete  loss.  If  the 
fruit  is  not  attacked  until  late,  it  may  remain  upon  the 
tree,  but  becomes  brown  spotted  and  finally  cracked.  On 
both  leaves  and  fruit  anthracnose  can  be  controlled  by  the 
use  of  Bordeaux  mixture.  A  rot  of  the  tree  trunk  is  caused 
by  Pythiacystis,  and  a  leaf-spot  by  Mycosphaerella.  ^^^ 

BANANA  AND  PLANTAINS 

Wilts  ^^^'  ■''^^  bacterial  and  fusarial,  are  of  wide  distribution. 
One  of  these  is  said  to  have  caused  the  abandonment  of 
nearly  20,000  acres  of  bananas  in  Panama. 

Anthracnose  (Gloeosporium  musarum  C.  &  M.)  frequently 
develops  on  ripe  fruit  in  the  market,  but  really  does  but  little 
injury. 

CACAO  '«! 

This  important  crop  is  subject  to  numerous  destructive 
diseases ,  the  most  serious  of  which  are :  Canker  and  Pod 
black-rot,  due  to  Phytophthora;  Die-back  due  to  Diplodia; 
Pink-disease  (Cortidum)  which  kills  even  large  branches, 
and  Witches-broom  {Colletotrichum).  Other  cankers  are 
caused  by  Nectrias. 

CITRUS  FRXnTS  ^^^ 

Brown-rot  ^-'^  {Pythiacystis  dtrophthora  S.  &  S.). — This 
disease  has  caused  a  very  considerable  loss,  30  per  cent  in 
some  cases,  in  California  but  the  real  origin  of  the  trouble 
135 


136 


Diseases  of  Economic  Plants 


was  not  known  until  1906  or  1907.  It  chiefly  affects  the 
fruit  after  it  has  been  packed  and  shipped  to  market,  al- 
though the  infection  takes  place  in  the  orchard  or  packing- 
house, where  the  disease  is  largely  disseminated  by  the  fruit 
washers. 

The  rot  has  a  peculiar  characteristic  rancid,  penetrating 
odor,  and  its  presence  is  further  indicated  by  the  prevalence 


Fig.  70. 


Brown-rot  of  lemons,  showing  white   growth  of   the 
fungus.    After  R.  E.  Smith. 


of  small  flies  in  boxes  where  there  is  diseased  fruit.  One 
affected  fruit  in  a  box  communicates  disease  to  the  whole. 

Brown-rot  is  found  in  nearly  pure  condition  on  the  fruit  in 
the  orchard,  especially  on  fallen  fruit  or  on  fruit  hanging  low 
on  the  tree.  It  is  most  prevalent  in  wet  weather  or  on  low 
ground  after  irrigation.  The  fungus  is  visible  to  the  eye  in 
the  packing-house,  as  a  mass  of  white  filaments.  It  is  spread 
by  contact  alone. 

Orchard  infection  can  be  controlled  by  the  use  of  a  heavy 
mulch  under  the  trees,  either  straw  or  a  heavy  cover  crop. 


Tropical  Fruits  137 

In  the  packing-house  the  use  of  disinfectants  in  the  washer 
prevents  trouble;  one  pint  of  formaUn  to  1250  gallons  of 
water,  or  1  pound  of  copper  sulfate  to  625  gallons  of  water. 

Cottony-rot  ^'^-  (Sderotinia  libertiana) .  —  The  fungus  on 
lemons  is  identical  with  that  of  lettuce  drop,  and  its  mycelium 
and  sclerotia  appear  as  described  under  that  disease.  The 
decay  spreads  rapidly  from  fruit  to  fruit  in  storage,  and  the 
loss  is  consideral^le.  Twig,  blossom,  or  seedling  infection  of 
oranges  or  lemons,  accompanied  by  gummosis,  also  occurs. 
Disinfection  of  the  fruit  with  1/50  per  cent  solution  of  copper 
sulfate  is  employed. 

Canker  *  ^^^-492  [Pseudomonas  citri  Hasse) .  — •  Citrus  canker 
is  one  of  the  most  destructive  diseases  introduced  into  the 
United  States  in  recent  years.  Its  nature  was  first  pointed 
out  by  Hasse  in  1915.  Before  that  time  it  was  thought  to  be 
caused  by  fungi  and  was  confused  with  citrus  scab.  The 
origin  of  the  disease  is  obscure.  It  was  first  described  from 
the  southernmost  island  of  Japan  in  1899  on  navel  oranges, 
where  it  was  undoubtedly  introduced  from  South  China. 
About  1910-11  citrus  canker  was  introduced  directly  from 
Japan  into  Texas  on  the  trifoliate  orange  and  on  nursery 
stock.  In  a  short  time  it  was  carried  into  other  Gulf  states 
on  infected  plants,  imported  directly  from  Japan  and  in- 
directly from  Texas,  so  that  by  1914  it  had  assumed  the 
aspects  of  an  epidemic  in  certain  parts  of  Florida,  Alabama, 
Mississippi,  Louisiana,  and  Texas.  About  the  same  time 
outbreaks  were  reported  from  two  areas  in  the  Transvaal, 
South  Africa,  the  Philippine  Islands,  and  later  from  North 
Australia;  originating  in  impoi-tations  from  Japan. 

Citrus  canker,  while  primarily  a  leaf  spot,  may  attack  parts 
of  the  tree  above  ground.  On  the  leaves,  the  young  spots 
usually  appear  on  the  under  side  as  small,  yellow,  translucent, 
oily  pimples.  Later  they  rupture  to  form  brown,  raised, 
corky  spots  with  an  oily  outline,  and  sometimes  a  wide, 
yellow  margin.  The  spots  break  through  to  the  upper  side 
of  the  leaf.  The  young  spots  on  the  twigs  and  branches  are 
*  Prepared  by  d.  L.  Peltier. 


138  Diseases  of  Economic  Plants 

similar  to  those  on  leaves,  but  usually  they  become  more 
corky  and  have  a  tendency  to  girdle  the  twig  or  branch.  On 
the  fruit  the  old  cankers  are  superficial  and  very  corky. 

Infection,  in  the  absence  of  wounds,  takes  place  through 
the  stomata.  The  period  of  incubation  varies  from  two  or 
three  days  to  several  weeks.  The  factors  favoring  infection 
are  a  high  temperature,  a  relatively  high  humidity,  and  a 
rapidly  growing  plant.  The  organism  survives  the  colder 
months  in  the  spots  on  the  twigs  and  branches.  Under  cer- 
tain conditions  the  organisms  may  lie  dormant  in  the  bark 
for  several  months. 

Pseudomonas  citri  has  a  wide  range  of  Rutaceous  hosts, 
including  all  the  plants  and  hybrids  of  the  genus  Citrus, 
although  some  show  considerable  resistance.  The  order  of 
susceptibility  of  the  more  important  commercial  citrus 
fruits  and  stocks  is  provisionally  as  follows:  grape  fruits, 
trifoliate  oranges,  lemons,  sour  oranges,  sweet  oranges,  limes, 
citrons,  mandarin  oranges,  and  kumquats.  Several  new 
introductions  of  citrus  fruits  and  hybrids,  originated  by 
Swingle,  show  considerable  resistance  and  promise  to  super- 
sede the  more  susceptible  fruits  in  some  instances. 

Infected  nursery  stock  was  wholly  responsible  for  the 
spread  of  citrus  canker  from  state  to  state.  However,  owing 
to  rigid  quarantine  measures,  further  danger  from  this  source 
appears  to  be  eliminated.  The  combination  of  wind  and 
rain  is  most  important  in  the  spread  of  canker  from  tree 
to  tree;  other  agents  are  dust,  insects,  birds,  man,  and  other 
animals. 

Owing  to  the  rapidity  with  which  citrus  canker  spreads  and 
its  menace  to  the  citrus  industry  of  the  Gulf  states,  drastic 
measures  for  its  control  were  adopted  in  1914-15  in  all  the 
Gulf  states.  These  consisted  in  burning  all  infected  trees 
as  soon  as  they  were  found. 

The  number  of  infected  citrus  trees  found  in  Florida  in 
August,  1914,  was  1313.  During  1918  only  15  were  found, 
and  in  1919  only  4  infected  trees.  Few  possible  centers  of 
infection  remain  in  the  United  States. 


Fig.  71.  —  Citrus  canker.     After  Webber. 


140 


Diseases  of  Economic  Plants 


Scaly-bark  ^^^  {Cladosporiimi  herbarum  Lk.  var.  dtricolum 
Faw.).  —  Small,  circular,  or  oval,  rusty-colored  spots  with 
well-defined  margins,  on  both  bark  and  fruit,  characterize 
this  disease.  The  bark  cracks  and  forms  scales.  The  spots 
are  at  first  scattered,  but  in  time  coalesce  and  form  large  areas 
upon  the  branches  and  trunk,  giving  it  a  scaly  appearance. 


Fig.  72.  —  Scaly-bark  injury  to  fruit.    After  Stevens. 


Similar  injury  also  occurs  on  the  fruit  (Fig.  72).  Sweet 
oranges  are  most  affected,  the  fruit  ripening  prematurely. 

Top  working  is  recommended,  also  heading  back  and 
painting  the  trunk  and  the  stumps  of  the  branches  with 
carbolineum  and  water  equal  parts. 

Gummosis. —  Several  diseases  recognized  by  the  exuda- 
tion of  gum  from  the  trunks  and  l)ranches  of  the  trees  are 


Tropical  Fruits 


141 


called  "gum  diseases."  Their  causes  are  not  definitely 
known;  by  some  they  are  attributed  to  mechanical  injury 
alone;  by  others  to  poor  cultivation  or  water  injury  in  ir- 
rigation; by  others  to  the  presence  of  soil  around  the  trunk; 
by  still  others  to  fungi. 

.  Blue-mold  rot  ^"^  (Penicillium  italicum  Wehni.,  antl  Penicil- 
lium  digitatum  (Fr.)  Sacc).  —  This  decay  of  citrus  fruits  in 
transit  from  California  causes  a  loss  estimated  in  1908  as 
being  between  $500,000  to  $1,500,000  annually.  Careful  in- 
vestigations of  Powell  and  his  assistants  have  shown  that  the 


lui.  73.  —  Two  forms  of  blue-mold:  at  left,  Penicillium  italicum;  at 
right,  P.  digitatum.    After  R.  E.  Smith. 

chief  trouble  results  from  wounds  on  fruit  in  handling,  which 
thus  provide  an  entering  point  for  the  fungus.  Without  me- 
chanical injury  no  decay  from  blue-mold  can  occur.  Hence 
the  method  of  control  is  painstaking  care  in  handling  the 
fruit  to  prevent  bruising  or  puncturing  the  skin. 

Black-rot  ^"'^  (Alternaria  citri  Pierce).  —  This  disease  was 
described  and  its  cause  given  by  Pierce  in  1902.  It  attacks 
only  the  navel  orange,  causing  from  2  to  5  per  cent  loss 
of  the  whole  crop.  It  is  easily  recognized  by  the  prema- 
ture ripening  which  it  induces,  and  by  the  deep  red  color 
and  extra  large  size  of  the  fruit.  The  diseased  fruits  are 
very  conspicuous  on  the  trees  before  the  main  crop  has  col- 


142 


Diseases  of  Economic  Plaiits 


ored.  A  considerable  portion  of  the  "June-drop"  is  caused 
by  this  disease. 

The  spores  of  the  fungus  gain  entrance  through  sHght 
imperfections  of  the  skin  at  the  navel  end,  producing  de- 
cayed areas  under  the  skin. 

All  diseased  fruit  should  be  collected  and  burned  or  buried 
deeply. 

Scab  {Cladosporium  citri  Mass.).  —  Scab  has  been  known 


Fig.  74.  —  Scab  of  the  sour  orange.    After  Hume. 


for  twenty  years,  and  occurs  on  the  sour  citrus  fruits,  such 
as  the  pomelo,  kumquat,  and  soin-  orange. 

The  disease  attacks  the  young  leaves,  twigs,  and  fruit, 
and  causes  them  to  produce  conspicuous,  warty,  corky 
growths,  that  give  a  rough,  uninviting  appearance.  Often 
the  leaves  are  twisted  and  drawn  out  of  shape.    The  warts 


Tropical  Fruits 


143 


are  at  first  yellowish,  l)ut  as  the  disease  advances  they  become 
almost  black,  antl  finally  crack  open. 

Ammoniacal  copper  carbonate  or  Bordeaux  mixture  will 
prevent  scab. 

Anthracnose,  wither-tip  {CoUetotrichum  glaeosporioides 
Penz.).  —  In  this  disease  the  leaf  spots  are  circular  in  out- 
line, yellowish  in  color,  and  bear  the  small  dark  filaments  and 
spores  of  the  causal  fungus. 
Terminal  twigs  shed  their 
leaves  and  die. 

The  disease  also  occurs 
upon  the  fruit  of  various 
citrus  trees.  Rolfs  noted 
its  attack  upon  the  lemon, 
where  it  caused  the  fruit 
to  fall  prematurely,  and 
Hume  reports  that  it  may 
occur  upon  the  pomelo 
either  before  or  after 
the  fruit  is  picked.  The 
brownish  spots  enlarge  with 
age  and  become  dirty 
black  in  color.  The  fun- 
gus invades  the  interior  of 
the  fruit  as  well  as  the  rind. 

In  all  cases  the  diseased  parts  should  be  cut  out,  care  being 
taken  to  cut  far  enough  back  to  remove  all  injured  parts; 
also  affected  fruits  should  be  removed  and  destroyed.  Spray- 
ing with  Bordeaux  mixture  controls  the  disease  upon  the 
fruit. 

Root-rot  (Phijtophthora  terrestria  Sherb.).  —  The  first  symp- 
toms are  abundant  exudations  of  gum  upon  the  trunk  of  the 
tree;  at  the  same  time  the  bark  develops  brownish  patches, 
which  are  thrown  off,  followed  ])y  other  patches.  The  tree 
appears  to  lack  nutrition,  the  leaves  becoming  yellow,  scanty, 
and  small.  Though  the  trees  heav  considerable  fruit,  the 
amount  of  damage  in  Florida  was  estunated  in  1896  to  be 


Fig.  75.  —  Orange  leaves  showing 
spots  caused  by  anthracnose.  Af- 
ter Hume. 


144  Diseases  of  Economic  Plants 

$100,000  annually.  Resistant  stock  should  be  used;  diseased 
parts  should  be  excised,  and  antiseptics  applied. 

Die-back  is  characterized  by  gum  pockets,  stained  terminal 
branches,  ammoniated  fruits,  bark  excrescences,  and  multiple 
buds.     The  disease  is  important  but  the  cause  is  unknown. 

Melanose  {Phomopsis  dtri  Faw.)  is  a  disease  of  foliage, 
young  twigs,  and  fruits,  in  which  small,  dark,  elongated  spots 
are  produced.    Weak  Bordeaux  mixture  should  be  used. 

Blight,  with  wilting  of  foliage  and  death  of  twigs  and 
branches,  is  of  unknown  cause.  In  many  ways  it  resembles 
peach  yellows. 

Minor  diseases 

Citrus-knot  {Sphceropsis  tumefaciens  Hed.),  troublesome 
in  Jamaica,  and  once  found  in  Florida;  various  leaf-spots; 
Sooty-mold  ^™'  ^^^  consisting  of  a  black,  superficial  fungus 
{Capnodium) ;  Algal  leaf-spot  produced  by  Cephaleuros 
virescens;  Crustose  lichens;  Dodder  and  Mistletoe,  occa- 
sionally attacking  citrus  fruit  trees;  Sour-rot  of  lemons 
(Oidium  citri-cmrantii) ,  also  called  slimy-rot  and  watery- 
rot  occurring  during  storage;  Crown-rot  (Sderotimn  rolfsii); 
Wood-rot  due  to  several  large  fungi ;  Die-back  and  stem-end- 
rot  (Diplodia),  and  Pink-disease  {Corticium)  are  of  minor 
importance. 

COCOANUT 

Bud-rot  ^^"^  {Bacillus  coli  (Esch.)  Mig.)  is  the  most  seri- 
ous disease  of  this  palm.  It  is  of  wide  and  growing  dis- 
tribution in  the  American  and  Eastern  tropics.  An  annual 
loss  of  £4500  is  reported  from  one  plantation  in  Jamaica. 
A  soft  rot  occurs  in  the  terminal  bud,  the  growing  point,  re- 
sulting in  the  death  of  the  tree.  Badly  diseased  trees  and  all 
infected  refuse  should  be  burned. 

COFFEE 

RuSt  (Hennleia  vastatrix  B.  &  B.).  —  This  most  destruc- 
tive coffee  disease,  believed  to  have  spread  to  coffee  from 


Tropical  Fruits  145 

some  weedy  Rubiaceous  host,  is  widely  present  through  the 
Old  World.  It  was  introduced  into  Porto  Rico  some  years 
ago,  but  prompt  recognition  and  effective  action  by  the 
Porto  Rican  Experiment  Station  exterminated  it  in  the 
Western  Hemisphere. 

Viruela  {Stilhella  flnvida  (Cke.)  Kohl).  —  This  is  the  most 
serious  coffee  disease  of  the  Western  Hemisphere,  causing 
circular,  decayed,  tan-colored  leaf-spots,  leading  to  rapid 
defoliation. 

Leaf-spot  (Cercosporn  cojfeicola  B.  &  C).  —  Numerous, 
circular,  brown  spots  occur,  causing  leaf-fall.  The  fungus 
grows  also  on  the  berries.  Other  leaf-spot  fungi  are  Col- 
letotrichum,  Gloeosporium,  Anthostomella,  Henderson ia  and 
Rhabdospora. 

Leaf -rot  "  (Corficium  koleroga  (Cke.)  v.  Hohn.).  —  The 
causal  fungus  grows  on  the  stems,  leaves,  and  fruit,  spread- 
ing as  a  smooth,  tissue-like,  whitish  film.  Rot  of  the  affected 
parts  follows. 

Stem-disease  (Necator  decretus  Mass.).  —  Minute  orange 
spots  are  produced. 

Root-rot  due  to  various  fungi  is  destructive. 


FIG  1*'*' 

Fruit-rot  (Colletotrichum  carica  S.  &  H.).  —  This  disease, 
first  described  in  1909,  produces  sunken,  rotten,  more  or  less 
circular  fruit  spots,  nearly  always  covered  with  a  white 
mass  of  fungous  mycelium.  As  the  spots  grow  older  they 
bear  numerous  pustules  of  the  salmon-pink  color  characteris- 
tic of  the  spores. 

The  amount  of  damage  caused  is  very  great  by  reason 
of  premature  falling  of  the  fruit,  at  times  destroying  the 
whole  of  the  crop. 

Infected  fruit  should  be  gathered  and  destroyed  and 
the  bushes  should  be  given  a  dormant  spray  and  two  or  more 
applications  of  Bordeaux  mixture  when  in  foHage. 

Rust   (Phjsopella  fid   (Cast.)   Arth.).  —  This  rust  does 


146 


Diseases  of  Economic  Plants 


considerable  damage,  causing 
premature  falling  of  leaves.  The 
rust  appears  as  brown  spots 
upon  the  leaf. 

Leaf-blight  {Cercospora  bol- 
leana  (Thiim.)  Speg.).  — This 
blight  has  been  noted  in  the 
United  States,  though  but  slight 
attention  has  been  given  it.  It 
causes  injury  similar  to  that  of 


Fig.  76.  —  Fig  in  well-advanced    rust, 
of  fruit-rot.    Original. 


Other  diseases  of  the  fig  are: 
a  Rhizoctonia  leaf-blight;  a  root-knot  due  to  nematodes; 
Southern-blight  (Sclerotium  rolfsii) ;  Cankers  due  to  Mac- 
rophoma,  Libertella,  and  Tubercularia;  Limb-blight  due  to 
Corticium;  Root-rot  (Ozonium)  and  Yellow-rust  {Fusarium). 
Black-smut  ^^^  {Sterigmatocystis)  may  affect  as  high  as  15  per 
cent  of  the  fruits  in  some  instances. 


GUAVA 

Ripe-rot  {Glomerella 
disease  was 
described 
from  green- 
house mate- 
rial collected 
at  Washing- 
ton, D.  C, 
and  after- 
ward it  was 
reported 
from  Florida 
and  Cali- 
fornia. The 
affected 
fruit  shows 
circu lar, 


i  (G.  Del.)   Sheldon).  — This 


Fig.  77.  —  Guava  affected  with  ripe- rot.  After  Rumsey. 


Tropical  Fruits 


147 


brown  decayed  areas.     In  older  stages,  masses  of  salmon- 
colored   spores  are  visible  over  the  decayed   areas.     The 
entire  fruit  at  length  becomes  rotten,  wrinkled,  and  shrunken. 
Algal  leaf-spot  {Cephaleuros  virescens)  is  common. 

LOQUAT 

Scab  (Fusicladium  dendriticum  (Wallr.)  Fcl.,  var.  eriobo- 
trycB  Scalia.).  —  In  the  western  part  of  California  scab  is 
reported  as  serious  upon  both  fruit  and  leaves. 


MANGO 

Anthracnose  ^^^-  ^'^^  (Colletotrichum  glceosporioides  Penz.). — 
This  rot  of  the  fruit,  flowers,  and  leaves  resembles  bitter-rot  of 
the  apple,  and  causes  much  loss  in 
the  Caribbean  region,  in  Hawaii, 
and  the  Gulf  states. 

OLIVE 

Knot  {Pseudomonas  savastanoi 
EFS.).  —  Tubercles  or  galls  upon 
the  leaves  and  branches,  and  even 
upon  the  trunk  of  the  tree,  are  the 
first  signs  of  attack.  Upon  the 
leaves,  the  knots  are  always  small, 
particularly  if  they  are  numerous. 
Upon  the  small  twigs  the  knots 
attain  the  size  of  a  garden  pea, 
while  upon  the  trunk  they  become 
2-3  cm.  or  more  in  diameter  and 
finally  destroy  the  tree.  The  dis- 
ease was  noticed  in  CaUfornia  in 
1893  and  appears  to  be  confined 
to  a  very  small  range.  Excision 
should  be  practiced. 

Leaf-spot  {Cydoconium  oleagi- 
num  Cast). — According  to  Bioletti 


Fig.  78.  —  Olive  knot.    After 
R.  E.  Smith. 


148  Diseases  of  Economic  Plants 

this  disease  is  prevalent  in  certain  regions  of  California, 
occasionally  causing  the  leaves  to  turn  yellow  and  injur- 
ing the  appearance  of  the  fruit.  Usually  it  does  but 
little  harm.  Spots  2-4  mm.  in  diameter  occur  upon  the 
leaves.  They  are  composed  of  concentric  rings  of  different 
colors,  giving  them  somewhat  the  appearance  of  the  spots  on 
peacock  tail  feathers.  The  spots  on  the  fruit  are  smaller  and 
more  decidedly  brown  in  color. 

The  use  of  Bordeaux  mixture  checks  the  trouble. 

Sooty-mold  occurs  nuich  as  on  citrus  fruits  and  Root-rot 
(Ar7mllaria  mellea)  as  on  other  orchard  trees,  p.  51. 

PINEAPPLE 

Black-heart  {Thiehiriopsisparadoxa  (d.  Seyn.)  v.  Hohn).  ^ 
This  rot  of  fruit  may  be  found  in  abundance  in  any  market 
and  causes  the  loss  of  many  carloads  of  fruit.  It  usually 
begins  at  the  stem-end  and  progresses  through  the  center  of 
the  fruit  as  a  soft  rot,  in  later  stages  turning  black,  due  to  the 
formation  of  many  spores.  Other  fruit  rots  are  due  to 
Diplodia,  Trichosphseria,  Penicillium.  Other  pineapple  dis- 
eases are:  Rot  of  young  plants  due  to  soil  fungi.  Wilt  and 
Chlorosis. 

PLANTAINS.    See  banana. 

VANILLA 

Numerous  diseases  are  recorded  on  this  orchid.  The  most 
destructive  is  caused  by  Calospora  vanillce  Mass.,  which 
grows  on  stems  and  leaves,  and  eventually  kills  the  entire 
plant.  Other  parasites  are  Vermicularia,  Colletotrichum, 
Gloeosporium,  Uredo,  Uromyces  and  Nectria. 


VEGETABLE  AND  FIELD  CROPS  ^'--  ^" 

These  crops  cover  a  wide  range  in  cost  of  production ;  some 
being  grown  in  glass  houses  with  artificial  heat,  others  under 
canvas  in  cold  frames,  still  others  under  ordinary  field  condi- 
tions. With  crops  of  high  value,  corresponding!}'  expensive 
methods  of  disease  control  are  warranted,  while  with  the 
field  crops,  resort  must  be  to  spraying  or  to  less  expensive, 
general  methods  of  sanitation  and  field  practice. 

The  crops  following  are  arranged  alphabetically  by  their 
common  names,  except  that  several  crops  of  a  botanical 
famil}^  when  generally  affected  by  the  same  diseases,  for 
convenience  of  discussion,  are  grouped  together. 

ASPARAGUS 

Rust  i"^"!"''  (Pucdnia  asparagi  DC).  —  Asparagus  rust, 
though  observed  in  Europe  as  early  as  1805,  was  not  noted 
in  epidemic  form  in  the  United  States  until  1896,  when  it 
was  recorded  by  Halsted  as  occurring  in  several  New  Eng- 
land States.  In  1897,  though  it  had  passed  to  South  Carolina 
and  to  some  extent  westward,  the  interior  and  western  part 
of  the  United  States  seemed  still  free  from  it.  In  1898  it  was 
first  found  in  Michigan;  in  1899  in  Illinois,  Ohio,  and  Kansas; 
in  1900  in  Dakota,  Nebraska,  and  Texas,  completing  its 
westward  march  into  California  in  1900  or  1901.  Now  it  is 
found  in  every  state  where  asparagus  is  grown. 

Rust  usually  first  attracts  attention  by  its  effect  upon  the 
green  tops  which  redden  under  the  disease,  this  symptom 
appearing  at  any  time  after  lilossoming  or  coming  to  leaf. 
Diseased  areas  in  the  field  enlai'ge  rapidly,  and  soon  the 
affected  leaves  yellow  and  fall,  leaving  the  bare,  dead  stalks. 
Close  examination  in  the  field  shows  that  the  twigs  and 
leaves  bear  many  small  skin  blisters  (sori)  under  which  is  a 
149 


150 


Diseases  of  Economic  Plants 


mass  of  powder  nearly  the  color  of  iron  rust.  In  early  stages 
of  attack  these  blisters  are  few  and  scattered,  but  they 
rapidly  increase  in  number.  When  young,  the  skin  covering 
the  sori  is  unbroken ;  later  it  ruptures,  setting  loose  the  rusty, 
powdery  mass  of  spores  beneath.    This,  the  summer  stage,  is 

chiefly  responsible  for  the 
hibernation  of  rust  in  the 
East.  Later  in  the  season 
th(^  sori  become  black  in- 
st(^ad  of  rusty-colored,  thus 
constituting  the  winter 
stage  of  the  rust. 

In  the  spring  still  an- 
other stage,  the  spring 
stage,  may  occasionally  be 
seen,  though  it  is  rare  east 
of  the  Rocky  Mountains. 
This  consists  of  small, 
oval,  pale  spots  upon  the 
branches  or  leaves.  In  the 
centers  of  these  spots  small 
round  pustules  develop  in 
concentric  lines.  Soon 
each  pustule  opens,  con- 
stituting a  very  minute  cup 
which  is  sunken  into  the 
leaf.  From  these  cups 
issues  a  powder  quite  sim- 


FiG.  79.  —  Sori  ot  the  asparagus  rust 
upon  the  stems,  enlarged.    Original. 


ilar  to  that  from  the  sori 
of     the     summer     stage, 
though    more    orange    in 
color.     All  three  stages  of  rust  —  spring,  summer,  and  win- 
ter —  may  occur  simultaneously  upon  the  same  plant. 

The  disease  spreads  rapidly  throughout  the  field  during  the 
spring  and  summer  stages.  The  winter  stage  is  the  typical 
hibernating  condition  in  which  the  causal  fungus  may  rest  un- 
til the  following  spring  before  it  can  induce  further  infection. 


Vegetable  and  Field  Crops  151 

During  the  first  two  stages  spores  in  enormous  quanti- 
ties are  liberated  by  the  least  movement  of  the  plants,  by 
animals  or  wind,  and  the  spores,  carried  to  their  new  prey, 
produce  infection  if  conditions  of  moisture  are  present. 

While  the  salable  part  of  the  plant  is  not  attacked,  the 
green  part  is  largely  decreased,  so  that  the  amount  of  nutri- 
ment that  can  l)e  stored  away  in  the  underground  parts  is 
lessened.  This  results  in  diminished  vigor  and  productive- 
ness of  such  roots  the  following  season.  The  loss  may  range 
from  15  to  35  per  cent  of  the  crop  the  year  after  the  first 
attack,  while  in  three  years  the  more  susceptible  varieties 
may  be  so  nearly  destroyed  as  to  necessitate  the  abandon- 
ment of  the  beds. 

Rust  is  most  injurious  in  light,  dry  soil;  irrigation  is,  there- 
fore, beneficial.  Dew  has  been  found  to  favor  rust;  there- 
fore shaded,  dewy  localities  should  be  shunned,  as  should  also 
rows  running  at  right  angles  to  the  prevailing  winds.  Clean 
culture  methods,  cutting  and  burning  all  tops  in  the  fall,  and 
destroying  all  wild  asparagus,  aids  in  the  prevention  of  rust. 

The  Palmetto  varieties  are  quite  resistant  and  offer  a 
solution  of  the  rust  problem  in  some  localities.  Careful 
breeding  has  given  rise  to  several  strains  known  as  "  Washing- 
ton asparagus"  that  are  highly  resistant.  In  dry  climates 
dusting  with  sulfur  150  to  200  pounds  per  acre,  about  three 
weeks  after  cutting  is  finished  and  l^efore  the  rust  appears, 
is  beneficial.  It  is  best  to  sulfur  early,  and  only  when  dew  is 
present. 

In  regions  subject  to  rain,  where  the  sulfur  treatment  is 
not  applicable,  three  sprayings  with  sulfur-soda  soap  are 
recommended:  first  in  July,  other  applications  at  intervals  of 
three  weeks.  In  New  York  three  sprayings  with  Bordeaux 
mixture  with  rosin  added  as  an  adhesive  gave  a  gain  of 
S132.75  per  acre. 

Minor  diseases 

Anthracnose  (CoUetotrichum  sp.)  is  known  by  its  numerous 
black  acervuli  borne  in  a  blanched  background  upon  the 


152 


Diseases  of  Economic  Plants 


stem.  It  develops  late  in  the  season.  The  name  Leopard- 
spot  is  strikingly  suggestive  for  another  disease  that  produces 
long,  irregular  spots,  ashen  in  color,  with 
dark  borders.    No  treatment  is  known. 

BEAN  ^-^^ 

Pod-spot  anthracnose  ^^^-i^"-  '^^-  '^^ 
{Colletotrichum  lindemuthianum  (S.  & 
M.)  B.  &  C).  —  First  described  in  1878 
in  Germany,  this  disease  is  widely 
known  and  is  especially  destructive.  It 
develops  so  rapidly  that  beans  delivered 
to  the  cars  for  shipment  in  apparently 
healthy  condition  may,  upon  arrival  at 
their  destination,  be  quite  badly  spotted. 
The  loss  is  often  20  per  cent,  and  occa- 
sionally a  total  loss  is  reported.  Upon 
the  pods  the  disease  appears  as  dark- 
colored  spots,  usually  sunken,  varying 
in  size  from  1-10  mm.,  or  more  if  sev- 
eral spots  coalesce.  The  border  of 
the  spot  is  often  tinged  with  red, 
the  center  rust-colored.  Old  pod -spots 
overlying  seeds  within  cause  spots 
upon  these  seeds.  The  pod-spots  are 
much  more  noticeable  and  unsightly 
upon  light-colored  than  upon  green 
beans. 

Similar   spots   are   found   upon    the 
stems  and  leaves.    They  are  especially 
noticeable    upon     young    stems    still 
blanched  and  upon  the  seed  leaves.    On 
Fig.  80.— Anthracnose  older  leaves  they  may  appear  upon  the 

spots  upon  bean  pods,  ^^j^s,  blackening  and  killing  them  and 

After  btewart.  , ,      ,      j. 

the  lear. 

The  wax  varieties  are  especially  susceptible,  while  lima 

beans  are  quite  resistant.    The  Well's  Red  Kidney  also 


Vegetable  and  Field  Ci 


153 


shows  valuable  resistance.    It  is  claimed  that  resistance  is  a 
dominant  Mendelian  character. 

The  fungus  is  carried  to  fields  largely  by  diseased  seeds; 


Fig.  81.  —  Bean  anthracnose  upon  stem  and  leaves  of  young 
plants.     After  Whetzel. 


by  beans  bearing  the  spots  above  mentioned.  Such  seeds 
result  in  infected  seedlings  which  serve  as  a  multiplying 
medium  for  the  fungus  and  result  in  its  spread  and  general 
attack  upon  the  field. 


154  Diseases  of  Economic  Plants 

In  fields  where  the  disease  is  well  established  upon  stems 
and  leaves  the  damage  is  great  in  loss  of  starch-producing 
power.  Still  greater  loss  follows  from  the  spread  of  the 
disease  to  the  pods,  the  unsightliness  of  the  spotted  pods 
greatly  injuring  their  salability. 

Since  the  spores  are  spread  only  when  they  are  wet, 
handling  or  disturbing  the  vines  in  any  way  while  the  dew 
or  rain  is  still  upon  them  should  be  avoided.  Seeds  already 
bearing  the  fungus,  i.  e.,  spotted  seeds,  should  never  be 
planted,  since  they  not  only  raise  sick  plants,  but  also  carry 
the  disease  to  the  field  to  infect  other  plants.  One  infected 
seed  may  carry  contagion  to  the  field.  Spraying  is  not  effec- 
tive. Since  no  remedy  is  at  hand  except  the  use  of  healthy 
seed,  the  greatest  care  should  be  given  to  this  point.  Home, 
fall-grown  seed  known  to  be  free  from  disease  is  preferable 
to  seed  of  unknown  origin.  If  a  few  seeds  known  to  be  free 
from  disease  can  be  secured  and  multiplied  in  a  special  seed 
plot,  they  will  give  clean  seed  for  future  use.  Clean  culture, 
the  removal  from  the  field  and  destruction  of  diseased  stalks 
and  plant  parts,  eliminates  a  source  of  spring  infection  which 
may  be  important. 

■  Rust  ^■''^'  ''^'^  {Uromyces  appendiailahis  (Pers.)  Link).  — • 
This  rust  may  be  recognized  by  its  sori  upon  the  leaves  and 
occasionally  upon  other  structures.  The  sori  appear  at 
first  as  blisters  of  pinhead  size,  covered  by  the  epidermis  of 
the  plant.  Later  this  covering  ruptures  and  discloses  a 
mass  of  spores  the  color  of  iron  rust,  or  later  in  the  season 
chestnut-colored,  which  fall  away  in  quantity,  smudging 
the  leaf  and  spreading  the  disease.  The  upper  side  of  the 
leaf  opposite  a  sorus  usually  shows  a  spot,  pallid,  yellowish, 
lacking  in  true  leaf-green  color.  Sori  are  sometimes  foimd 
upon  the  upper  surface,  but  not  so  frequently  as  upon  the 
lower. 

Rust  usually  develops  somewhat  late  in  the  season  and 
therefore  is  not  so  destructive  as  are  many  of  the  other  bean 
troubles,  though  in  certain  localities,  e.  g.,  in  Virginia,  the 
crop  is  sometimes  completely  destroyed. 


Vegetable  and  Field  Crops 


155 


It  is  reported  upon  many  species  of  true  beans  (Phaseolus) 
and  upon  related  genera  as  Vigna,  Falcata,  Strophostyles. 
Where  the  disease  proves  destructive,  the  use  of  resistant 


31 


Fig.  82. 


Bean  rust  upon  leaf  and  pods;  note  the  numerous  sori  upon 
both  surfaces.    After  Beach. 


varieties,  clean  culture,  and  the  destruction  of  all  wintering 
forms,  is  advisable. 

Blight  ^^^  {Pseudomonas  phaseoli  EFS.). — Beans  of  va- 
rious kinds  are  subject  to  a  blight  which  manifests  itself 
upon  the  pod,  leaf,  or  stem.  It  has  been  reported  from 
various   states,    from   Canada,    is   widely   distributed,    and 


156 


Diseases  of  Economic  Plants 


often  quite  destructive.     It  was  first  observed  by  Beach  in 
New  York  in  1892. 

Usually  the  leaves  are  the  parts  first  attacked.  Here 
large,  translucent  patches,  brown  in  color,  are  produced. 
These  spots  later  dry,  become  papery  in  texture,  and  rup- 
ture, leaving  the  foliage  ragged  and  torn.  Later  infection 
spreads  to  the  pods,  which  develop  watery,  ulcer-like  spots 
without  definite  boundary,  similar  to  those  upon  the  leaves, 
though  often  amber-coated.  Attack  upon  young  pods  kills 
them. 


Fig.  83.  —  Blight  of  bean  leaves.    After  Fulton. 


This  disease  is  carried  over  the  season  largely  by  infected 
seed  and  is  conveyed  from  plant  to  plant  in  the  field  by 
insects. 

Diseased  seed  and  seed  from  fields  bearing  the  disease 
should  be  avoided,  and  clean  culture,  including  the  burning 
of  all  infected  plant  parts,  should  be  practiced.  The  follow- 
ing list  shows  the  variation  in  resistance,  the  least  susceptible 
being  placed  first  and  the  most  susceptible  last:  Schindler's 
Round  Pod  Wax,  Refugee  Wax  Burpee's  White  Wax, 
Grenell's  Rust-proof  Golden  Wax,  Wardwell's-Kidney  Wax, 
Dwarf  German  Black  Wax,  Early  Valentine. 


Vegetable  and  Field  Crops 


157 


Stem-rot,  pod- 
rot  1^'  ''-  1^3  (Cortin 
cium  vagum).  — 
This  disease  is 
manifest  in  three 
forms: 

1.  Damping-off 
of  seedHngs.  See 
damping-off. 

2.  Dry-rot  of  the 
stem.  In  this  con- 
dition the  tissue  is 
dead,  discolored, 
and  dry-rotted  at 
from  2-5  cm.  above 
the  ground.  The 
rot  extends  to  the 
pith  and  usually 
encircles  the  stem, 
and  thus  so  weak- 
ens the  plants  that 
they  are  often 
broken  by  the  wind. 
In  any  event  they 
soon  wilt  and  die. 

3.  As  brown 
sunken  areas  upon 
pods,  penetrating  to 
and  discoloring  the  seeds. 


Fig.  85.  —  Blight  upon  bean  seeds.    Alter  Clinton. 


Fig.  84.  —  Blight  of  the  bean.    After  Halsted. 

The  germination  of  the  seed  is  not 
stopped  by  this 
attack,  and  a 
fruitful  source 
of  dissemina- 
tion is  thus  af- 
forded. Such 
seeds  should  be 
avoided. 


158  Diseases  of  Econo7nic  Plants 

Downy-mildew  ^^^'  ^^-^  (Phytophthora  phaseoli  Thaxt.).  ^ 
Downy-mildew  is  a  northern  disease  regarded  by  Halsted 
as  the  most  serious  disease  of  the  lima  bean.  It  was  first 
recorded  by  Thaxter  in  1889. 

Upon  the  pods  growths  of  dense,  woolly-white,  irregular 
patches  appear.  These  consist  of  myriads  of  spore-bearing 
hyphse  of  the  causal  fungus,  laden  with  their  spores.  The 
mildew  also  attacks  young  shoots,  petioles,  flower  clusters, 
and  leaves,  causing  them  to  develop  in  dwarfed,  imperfect 
fashion  and  destroying  their  value.  The  spores  are  largely  car- 
ried by  nectar-seeking  insects,  which  accounts  for  the  preva- 
lence of  flower  infection.     Spores  are  also  carried  by  wind. 

Even  in  a  season  favorable  to  the  development  of  the 
disease,  thoi-ough  use  of  Bordeaux  mixture,  three  sprayings, 
will  insure  the  crop.  The  destruction  of  infected  trash  is 
advisable. 

Southern-blight  {Sclerotium  rolfsii). — The  symptoms 
are  wilting  of  the  leaves,  temporary  recovery,  yellowing, 
dying,  and  eventually  dropping.  The  fungus  usually  at- 
tacks the  plant  just  below  the  surface  of  the  ground,  in- 
vades the  cambium,  and  destroys  it.  For  further  details,  see 
pepper. 

Pod-blight  ^'^^  (Diaporthe  phaseolorum  (C.  &  E.)  Sacc, 
Phomopsis).  —  This  destructive  lima-bean  blight  was  first 
recognized  in  New  Jersey  in  1891,  and  is  now  known  gen- 
erally in  the  East,  producing  upon  pods  and  leaves  large, 
brown  patches,  with  the  pycnidia  arranged  in  concentric 
circles.  When  the  disease  is  prevalent,  the  pods  fail  to 
mature  their  seeds. 

Clean  seed  should  be  used  and  the  plants  sprayed  with 
Bordeaux  mixture. 

Drop  ^•"'  (Sclerotinia  lihertiana) .  —  This  rot  is  reported  to 
cause  a  reduction  of  30  per  cent  in  yield  in  some  fields.  Loss 
of  nearly  $3,000  is  reported  on  one  30-acre  field  in  Virginia. 
It  may  develop  rapidly  in  transit,  and  thus  cause  secondary 
freight  losses.  Field  refuse  should  be  burned,  and  crop 
rotation  practiced.    See  also  lettuce, 


Vegetable  and  Field  Crops 


159 


^' 


Minor  diseases 

Orobanche  is  sometimes  parasitic  on  beans.  Sunscald  ^^^ 
produces  discoloration.  Powdery-mildew  (Erysiphe  polygoni 
DC.)  often  gives  a  rusty  color  to  the  pods.  Leaf-blotch 
(Cercospora  cruenta  Sacc.)  occurs  only  upon  the  foliage  as 
brownish  patches,  causing  the  ^ 

leaves  to  fall  away.    The  spots  ^^^'^ 

are  large,  angular,  and  limited  ^^,  ^ 

by  the  veins.    Leaf-spot  (Isar-  / 

iopsis  griseola  Sacc.)  is  chiefly 
limited  to  the  foliage,  produc- 
ing small,  angular  spots,  over 
the  under  surface  of  which  the 
fungus  forms  a  gray,  moldy 
covering.  It  has  been  ob-  .  ^L 
served  in  many  states,  and  is  "-'*'' 
most  injurious  in  the  South. ^'^' 
Wilt  due  to  Pseudomonas  sol- 
anacearum  has  also  been  re- 
ported. Root-knot  (nema- 
todes) is  injurious  in  some 
localities.  Streak.  —  Dark 
spots  occur  on  stems,  leaves, 
and  pods.  The  cause  is  un- 
known.    Mosaic  ^^  in  general 

character    resembles    tobacco  j,^^   gg  _  j^i,^^.^^^^  p^^^  ^l^^^. 
mosaic.    It  appears  to  be  of     ing  pod-blight.   After Halsted. 
wide  distribution  and  to  be 

communicated  through  the  seed.     Resistant  strains  should 
be  grown. 

BEET,  CHARD,  MANGOLD,  MANGELS 

Cercospora  Leaf-spot  ^^^~^^''  {Cercospora  beticola  Sacc).  ^ 
This,  one  of  the  several  leaf-spots  upon  the  beet,  is  very 
widespread  in  the  eastern  and  middle  states.  Very  few 
fields  are  entirely  free  from  it.  It  occurs  upon  all  varieties, 
but  is  especially  injurious  to  the  sugar  beet. 


'"-S 


160  Diseases  of  Economic  Plants 

The  round,  brownish,  purple-bordered  spots  turn  ashen 
in  the  center,  and,  when  mature,  often  become  so  thin  and 
brittle  as  to  drop  out,  leaving  ragged  holes.  The  sporiferous 
hyphae  upon  the  spot  centers  may  be  seen  with  a  good  lens. 

These  spots  frequently  destroy  the  greater  part  of  the 
green  tissue  of  the  leaf,  and  thus  its  value  to  the  plant  as  a 
sugar  producer,  or  even  cause  the  leaves  to  die,  in  which 
event  they  blacken  and  remain  standing  nearly  upright  upon 
the  crown.  The  death  of  the  older  leaves  causes  the  crown 
to  elongate,  suggesting  the  name  "pineapple  disease." 
Dry  weather  followed  by  a  damp  spell  favors  the  disease. 
Infested  refuse  in  manure  may  serve  to  spread  the  leaf-spot 
but  beet  tops  made  into  silage  do  not  carry  contagion. 

Sprayed  plants  in  New  Jersey  gave  a  much  cleaner  foliage 
and  yielded  480  pounds  of  root  as  against  380  pounds  from 
the  unsprayed  plants  from  an  equal  area,  a  gain  of  nearly 
26  per  cent.  While  partial  control  may  thus  be  had  by 
spraying,  the  cost  may  not,  however,  be  justified.  Crop 
rotation  and  deep  fall  plowing  should  be  practiced. 

Curly-top. ^^^'  ^''^'  -°^  —  The  first  symptom  appears  in  the 
inner  leaves,  which  curl  inward  from  the  entire  margin  toward 
the  midrib.  Soon  the  veins  become  knotted  on  the  dorsal 
surface.  Later,  the  entire  plant  is  stunted  and  shows  similar 
changes;  whole  leaves  curl  tightly  and  the  petioles  remain 
short  and  become  bent.  The  roots  develop  an  abnormal 
number  of  fine  rootlets,  leading  to  the  common  name  ''hairy- 
root."  (See  also  p.  162.)  They  are  also  tough  and  some- 
times present  a  blackened  area  or  cavity  within.  Curly-top 
occurs  annually  on  sugar  beets  in  Colorado,  Utah,  Idaho,  and 
California,  and  in  fact  in  all  states  west  of  Nebraska  where 
sugar  beets  are  grown.  In  some  years  thousands  of  acres  are 
completely  destroyed,  the  total  loss  during  the  last  sixteen 
years  being  estimated  at  $16,000,000.  Even  though  the  beets 
grow  to  fair  size,  impurities  lower  their  value  for  sugar 
production  and  their  seeding  power  is  injured.  The  disease, 
however,  is  not  seed-borne.  As  to  the  cause,  but  little  is 
definitely  known  beyond  the  fact  that  this  disease  can  be 


%J 

n  A 

^ 

ak^ 

Hi     <.- 

•*                                              -'*>, 

^HHHSii 

^ 

4 

r 

^ 

Fig.  87.  —  Curly-top.    After  Boncquet. 


162  Diseases  of  Economic  Plants 

conveyed  by  grafting,  but  otherwise  develops  only  after  the 
sting  of  a  leaf  hopper  (Eutettix  tenella)  that  has  been  in  con- 
tact with  beets  affected  with  curly-top.  Bacillus  morulans 
Bone,  has  been  associated  with  curly-top,  but  its  causal 
relation  not  demonstrated. 

Root-rot  ^^^  (Corticium  vaguni).  —  Beets  affected  with 
this  rot  usually  show  first  attack  at  the  bases  of  the  outer 
leaves,  which  turn  black.  The  stalks  weaken  and  allow 
the  leaves  to  fall  prostrate,  though  they  do  not  lose  their 
color  at  once.  The  disease  thence  passes  into  the  crown, 
turning  the  involved  parts  brown  and  later  leading  to  crack- 
ing of  the  root.  In  this  condition  the  mycelium  of  the 
fungus  is  clearly  evident  in  the  cracks.  Eventually  the 
whole  top  may  rot  off.  The  spread  is  rapid  from  plant  to 
plant  in  the  field.  Dry  or  cold  weather  may  so  retard  the 
invasion  that  the  plant  can  recover  if  not  too  badly  affected. 

The  disease  is  probably  the  same  that  has  been  destruc- 
tive to  sugar  beets  in  Germany.  It  has  been  reported  from 
several  places  in  the  United  States. 

Air-slaked  lime,  60  to  70  bushels  per  acre,  has  been  recom- 
mended. 

Phoma  Root-rot  ^^^  (Phoma  beta  (Oud.)  Frank.).  —  Upon 
the  roots  a  shrunken,  coal-black  discoloration,  extending 
sometimes  quite  to  the  center,  indicates  the  presence  of  this 
dry  rot.  No  disagreeable  odor  attends  the  rot.  Upon  the 
affected  surface  pycnidia  appear  as  very  minute  pustules. 
Upon  the  leaves  this  same  fungus  forms  large,  circular, 
dead  spots.  The  disease  may  also  appear  on  seedlings,  caus- 
ing damping-off. 

All  infected  leaves  should  be  removed  from  the  roots 
before  placing  in  storage. 

Root-knot  and  Hairy-root  (nematodes).-"^-  ^^*  —  Two  spe- 
cies of  nematodes  affect  beets,  one  of  which  produces  root- 
knot,  the  other  hairy-root,  both  of  which  are  quite  destruc- 
tive. Root-knot,  due  to  nematode-infection,  is  discussed  on 
p.  24.  Hairy-root  shows  first  symptoms,  as  the  hot  season 
begins,  in  a  wilting,  yellowing,  and  dying  of  the  outer  leaves, 


Vegetable  and  Field  Crops  163 

and  dwarfing  of  the  inner  leaves.  Dense  masses  of  fine  root- 
lets develop  below  ground,  giving  rise  to  the  common  name. 
The  really  distinctive  character  is  the  presence  of  numerous 
yellowish,  beadlike  objects,  a  little  over  a  millimeter  long, 
clinging  to  the  rootlets.  This  disease  has  been  very  destruc- 
tive in  Europe,  and,  introduced  into  the  United  States  prior 
to  1907,  is  established  in  several  districts  in.  the  West.  Fol- 
lowing is  a  partial  list  of  plants  known  to  be  susceptible  to 
hairy-root.  Those  marked  with  a  *  are  highly  susceptible. 
Alfalfa,  allseed,  barley,  bean,  dwarf  pea,  lima  bean,  garden 
beets,*  sugar  beets,*  Brussels  sprouts,*  cabbage,*  Chinese 
cabbage,*  cauliflower,*  celery,  crimson  clover,  white  clover, 
corn,  cress,*  dandelion,  green  foxtail,  hemp,  hops,  kale,* 
kohl-rabi,*  lentils,  yellow  lupine,  annual  meadow  grass, 
tall  meadow  oat-grass,  mustard,*  oats,  parsnip,  garden  pea, 
sweet  pea,  pink,  potato,  radish,*  rape,*  rutabaga,*  rye, 
sorghum,  spinach,  sunflower,  timothy,  turnip,*  vetch,  wheat. 

A  rotation  of  four  or  five  years  with  nonsusceptible  crops 
is  the  only  safe  procedure  with  infected  land.  Small  areas  of 
local  infection  may  be  eliminated  by  a  heavy  application  of 
unslaked  lime  well  mixed  into  the  soil. 

Black-root-"^  {Rheosporangium  aphanidermalus  Eds.). — 
Black-root  occurs  on  both  radish  and  beet,  causing  damping- 
off  and  a  browning  or  blackening  and  often  death  of  the  root. 
Disinfection  of  seed  is  advisable. 

Damping-ofif.  —  Damping-off  of  seedlings  near  the  surface 
of  the  ground  soon  after  they  come  up,  often  before  thin- 
ning, is  a  frequent  cause  of  loss.  The  leaves  yellow,  the 
roots  turn  brown,  and  the  plants  topple  over  and  die.  This 
is,  in  some  instances,  due  to  the  usual  causes  of  damping- 
off,  Corticium,  Pythium,  Phoma,  but  sometimes  to  a  heavy 
crust  formed  upon  the  soil,  thus  preventing  the  safe  emerg- 
ence of  the  seedling. 

Minor  diseases 

Scab  ^^^  {Actinomyces  scabies)  resembles  closely  the  scab 
of  the  Irish  potato.     It  usually   covers  more  completely 


164  Diseases  of  Economic  Plants 

the  surface  of  the  beet  than  in  the  case  of  the  potato,  and 
tends  more  to  form  corky  growths  upon  the  surface  than 
to  make  deep  cavities.  Beets  shoukl  not  be  grown  upon 
land  known  to  be  infested  with  the  potato  scab  or  to  have 
borne  a  badly  infected  crop  of  beets.    See  also  potato  scab. 

Bacterial  Leaf-spot  ^''"  {Pseudomonas  aptatum  (B.  &  J.). 
—  The  leaves  in  this  disease  bear  irregular,  dark  brown 
or  black  spots,  1  mm.-3  cm.  in  diameter,  chiefly  upon  the 
petiole,  midril),  and  larger  veins.  Occasionally  the  dis- 
coloration extends  along  a  vein  for  some  distance,  and  the 
tissue  on  either  side  becomes  l)rown  and  dry. 

The  disease  was  first  observed  by  Townsend  in  Utah  and 
Colorado,  and  its  bacterial  origin  was  demonstrated  by 
Brown. 

Rust  {Uromyces  hetce  (Pers.)  Kuhn)  has  long  been  known  in 
Europe,  where  it  was  studied  as  early  as  1869.  It  is  occa- 
sionally met  in  some  of  the  western  states  and  has  been 
reported  as  injuring  the  beet  in  market  gardens  in  California. 
It  is  recognized  by  the  characters  of  the  true  rusts,  i.  e., 
blisterlike  sori. 

Removal  of  the  leaves  bearing  the  spring  stage  and  spray- 
ing with  Bordeaux  mixture  has  been  recommended.  Af- 
fected leaves  used  as  feed  may  carry  the  disease  through 
the  manure  to  plants  of  the  following  season. 

White-rust  (Albugo  hliti  (Biv.)  Ktz.). — The  sori  are 
blisterlike,  as  in  the  true  rusts.  The  rupture  of  the  epidermis 
releases  masses  of  snow-white  spores. 

Soft-rot  ^^^  {Bacterium  teutlium  Met.)  was  prevalent  in 
Nebraska  in  1904.  Leaf-scorch.'-'^-  —  The  leaves  blacken 
and  die,  and  the  roots  are  small,  discolored,  and  poor  in 
sugar  content.  Crown-gall  and  Root-tumor  (Urophlyctis) , 
Downy-mildew  (Peronospora) ,  and  Drop  (Sclerotinia)  cause 
some  loss. 

BROCCOLI.    See  cabbage. 

BRUSSELS  SPROUTS.    See  cabbage. 


Vegetable  and  Field  Crops 


165 


BUCKWHEAT 

Blight  ^*'''  {Corticium  vagum),  causing  death  of  plants  in 
large  areas  in  the  field,  was  noted  in  North  Carolina.  Leaf- 
spot  {Septocylind]-'ium  rufomaculans  (Pk.)  P.  &  C.)  is  reported 
as  diminishing  the  yield  in  Connecticut.  Powdery-mildew 
{Erysiphe  polygoni)  is  of  slight  importance. 


CRUCIFEROUS  CROPS:  CABBAGE,  BRUSSELS  SPROUTS, 
CAULIFLOWER,  COLLARD,  TURNIP,  KOHL-RABI, 
KALE,   RAPE,   RADISH,   BROCCOLI,  RUTABAGA 

These  crop  plants  are  of  close  kinship  and  are  subject, 
essentially,  to  the  same  diseases.     The  more  important  of 
these  are  internal  parasites  from  the  soil,  hence  spraying  is 
of  less  benefit   than   with 
other  crops. 

,  Black-rot  -^^'-'^^'  ^-^'  ^^^'  ^^ 
{Pseudomonas  campestris 
(Pam.)  EFS.).  —  Not  only 
does  black-rot  destroy  the 
current  crop,  but  since  its 
causal  germ  remains  in  the 
soil,  it  seriously  endangers, 
if  it  does  not  quite  prohibit, 
the  subsequent  use  of  the 
same  field  for  susceptible 
crops.  Its  damage  to  cab- 
bage in  a  single  season  in 
two  counties  in  Wisconsin 
was  estimated  at  between 
$50,000  and  $60,000.  A 
large  per  cent  of  the  dam- 
age to  cabbage  in  storage  Fig.  88.  —  Cabbage  leaf  showing  an 
is  also  attributable  to  this       incipient  stage  of  black-rot.    The 

disease.       Cabbage,    kale,  f^^'''  ""^''^  ""*"'-^.  ^^*  f"^  ^"fs/'^ 

,  ,.      f    ,  ,       ,  .  the  veins,  is  progressing  toward  the 

rape,     broccoli,     kohl-rabl,  base  of  the  leaf .    After  Stewart  and 

Brussels    sprouts,  collards,  Harchng. 


ii 


166 


Diseases  of  Economic  Plants 


turnips,  rutabagas,  radish,  black  mustard,  charlock,  and 
other  members  of  the  cress  family  are  affected. 

Black-rot  was  first  noted  on  turnips  in  1892  in  Iowa,  and 
on  cabbage  in  1895  in  Wisconsin,  and  is  now  very  dis- 
astrous in  its  effects  in  practically  ail  sections  of  the 
United  States  east  of  the  Mississippi  River,  as  well  as  in 
the  more  western  states. 

Infection  arises  from  the 
causal  bacteria  which  are 
often  present  in  the  soil  from 
preceding  years.  These  bac- 
teria gain  access  to  the  drops 
of  water  at  the  water  pores 
on  the  leaf  edge.  The  first 
sign  of  the  disease  appears 
as  a  blackening  of  the  veins 
upon  the  edges  of  the  leaves. 
The  affected  region  rapidly 
enlarges,  the  blackening  ex- 
tending toward  the  stalk, 
and  throughout  the  vascular 
system.  Soon  this  blacken- 
ing reaches  the  stem  of  the 
plant  and  proceeds  up  and 
down  the  stem,  thus  gaining 
Fig.  89.  —  Portion  of  cabbage  stem  entrance  to  other  leaves, 
showing  blackened  veins.  Re-  gj^^u  reaching  the  entire 
drawn  after  Russell.  i      -      tt        n  i 

plant.    Usually  many  leaves 

are  infected  simultaneously.  Affected  leaves  soon  yellow 
and  wilt,  owing  to  the  obstruction  of  the  water  channels, 
then  dry,  become  parchment-like,  and  fall  to  the  ground. 
General  infection  of  the  plant  is  followed  by  death.  Reliable 
diagnostic  characters  are  the  blackened  vein  areas  of  the  leaf, 
blackened  veins  as  seen  in  cross  sections  of  the  leaf  stalk  or 
of  the  stem  of  the  plant.  Other  rots  may  supervene,  giving 
offensive  odors.  If  plants  with  the  smallest  amount  of  dis- 
ease are  placed  in  storage,  the  disease  continues  to  develop, 


Vegetable  and  Field  Crops 


167 


resulting  in  complete  loss.  The  bacteria  may  travel  upon 
seed  from  diseased  localities,  infect  the  young  plants,  and 
initiate  an  attack  in  a  new  locality.  Plants  shipped  across 
the  country  may  also  carry  infection. 

The  disease  may  be  carried  from  field  to  field  in  any 
plant  part  or  in  infected  soil,  upon  tools,  feet,  etc.,  and  espe- 
cially in  manure  that  has  become  infected  by  the  use  of 


Fig.  90.  —  Cauliflower  affected  with  black-rot. 
Original. 

diseased  plants  as  feed.  To  avoid  carrying  contamination 
to  near-by  fields  all  the  precautions  suggested  under  soil 
diseases  must  be  employed. 

With  infested  land  the  only  recourse  is  such  crop  rotation 
as  will  avoid  the  planting  of  a  susceptible  crop  for  a  period  of 
several  years.  Just  how  long  the  bacteria  can  remain  alive 
in  the  soil  is  not  known.  In  practicing  crop  rotation  for 
elimination  of  this  pest  all  cruciferous  weeds,  mustard,  shep- 
herd's purse,  etc.,  should  be  avoided,  since  they  are  sus- 


168 


Diseases  of  Economic  Plants 


ceptible  and  harbor  the  disease  just  as  effectively  as  would 


Since  the  seed  may  carry  the  bacteria,  it  is  well  to  soak 
them  for  fifteen  minutes  in  formalin,  one  teaspoonful  to  a 
half  pint  of  water,  to  kill  these  germs  and  thus  avoid  in- 
troducing the  disease  into  new  iocahties.  If  this  had  been 
done  in  earlier  years,  many 
counties  now  so  infected  as  to 
prohibit  cabbage  culture  would 
still  be  free  from  this  pest. 
Resistant  varieties  will  do 
much  to  solve  the  problem. 

The  cauliflower  is  affected 
in  much  the  same  way  as  the 
cabbage.  Local  infection  in 
the  head  often  produces  the 
effect  shown  in  Fig.  90. 

•  Club-root  2««-2ii'  227  (^pias- 
modiophora  brassicce  Wor.) .  — 
Club-root  is  practically  of 
world-wide  distribution,  and 
destructive  to  cabbage,  kale, 
cauliflower,  turnip,  rutabaga, 
collards,  Brussels  sprouts, 
radish,  stocks,  candytuft,  sweet 
alyssum,  and  upon  wild  crucif- 
erous plants,  shepherd's  purse, 
peppergrass,  pennycress,  black 
mustard,  charlock,  false  flax, 
hedge  mustard.  It  may  readily  be  recognized  by  the  en- 
larged growth  of  either  the  main  root  or  the  lateral  roots,  or 
both,  as  shown  in  the  accompanying  figure.  It  cannot  be 
confounded  with  any  other  disease  unless  that  caused  by 
eel  worms  (nematodes),  and  from  this  it  may  easily  be  dis- 
tinguished by  the  larger  club-root  galls. 

These  swellings  may  be  noted  in  the  seed  bed,  though  they 
are  usually  overlooked  until  they  enlarge  in  the  field.    They 


91.  —  Cabbage  club-root. 
Original. 


Vegetable  and  Field  Crops  169 

so  diminish  the  vigor  of  the  plant  that  it  assumes  a  sickly 
appearance,  ceases  to  develop,  and  fails  to  head.  The 
affected  parts  usually  succumb  to  offensive  secondary  rots, 
the  causal  organism  is  released,  and  the  soil  is  thus  infected. 

The  proof  of  the  parasitic  origin  of  this  disease  was  made 
by  Woronin  in  1873,  after  three  years  of  intensive  study. 

In  general  the  precautions  against  its  spread  are  those 
suggested  under  the  general  heading  of  soil  diseases.  All 
diseased  refuse  is  infective,  as  is  also  manure  to  which  it 
has  had  access.  Fields  which  are  diseased  remain  so  for 
several  years;  therefore  rotation  to  nonsusceptible  crops 
should  be  followed.  Seedlings  should  be  examined  care- 
fully to  guard  against  the  use  of  plants  from  an  infected 
seed  bed,  and  special  care  should  be  taken  to  avoid  infecting 
the  seed  bed  with  soil,  manure,  or  refuse.  Air-slaked  stone 
lime,  75  bushels  per  acre,  applied  each  year  some  weeks  be- 
fore planting,  has  given  beneficial  results.  In  New  York, 
where  90  bushels  of  shell  lime  were  applied  per  acre,  an  ex- 
cellent crop  was  grown,  while  upon  untreated  soil  only  60 
heads  were  cut  from  472  plants.  The  Hollander  and  the  blue 
or  red  varieties  of  cabbage  are  said  to  show  some  resistance. 

Root-knot  (nematodes) .  —  Root-knot  in  some  respects 
resembles  club-root,  but  with  smaller  swellings.  It  is  com- 
mon on  crucifers. 

Black-leg -^•'^' -^^  (P/?.oma  lingam  (Tode)  Desm.). —  Great- 
est injury  is  done  to  cabbage  and  cauliflower,  less  to  other 
crucifers.  Dark,  sunken  areas  occur  on  the  stems  near  the 
ground;  gradually  the  stem,  and  later  the  plant,  dies.  Spots 
may  also  appear  on  leaves  or  petioles.  The  presence  of  pyc- 
nidia  in  the  spots  is  the  really  distinctive  character.  The  dis- 
ease is  important  chiefly  in  the  East  and  North,  though  it  has 
been  reported  from  the  South  and  extreme  West,  as  well  as 
from  Europe  and  Australia.  Infection  may  be  carried  or  main- 
tained by  diseased  refuse  or  on  the  seed.  Seeds  should  be  dis- 
infected (pp.  240,  449),  and  healthy  soil  used  for  the  seed  bed. 

Black-mold  (Alternaria  brassiar  (Berk.)  Sacc).  —  Upon" 
the  cabbage,  cauliflower,  and  collard,  particularly  in  the 


170 


Diseases  of  Economic  Plants 


South,  this  mold  is  quite  destructive  both  in  the  field  and  in 
storage.  The  affected  spots  are  nearly  black,  circular, 
marked  concentrically,  and  are  not  definitely  bordered,  i.  e., 
they  shade  off  gradually  into  the  surrounding  healthy  tissue. 


Fig.  92.  —  Black-mold  on  oollard  as  seen  from 
upper  side  of  the  leaf.     Original. 

They  enlarge  sometimes  to  2-3  cm.  in  diameter.  The  tissue 
dries,  becomes  brittle,  and  often  falls  away,  leaving  ragged 
holes. 

In  many  instances  the  plants  die  or  fail  to  mature.  In 
storage  the  spots  continue  to  enlarge,  and  it  is  here  that  the 
greatest  loss  occurs.  Storage  houses  should  be  disinfected 
with  Bordeaux  mixture,  and  temperature  and  ventilation 
regulated  as  suggested  under  soft-rot,  p.  172. 

Drop -^^  {Sclerotinia  Uhertiana).  —  This  malady  is  dis- 
cussed luider  lettuce.     Upon  the  cabbage,  rape,  cauliflower, 


Vegetable  and  Field  Crops 


171 


and  radish  it  may  be  recognized  by  the  cotton-like  myceHum 
and  the  black  sclerotia  which  appear  in  advanced  stages  of 
disease.  It  is  particularly  troublesome  in  the  Southern 
states. 

A  form  of  this  rot  is  described  by  Hedgcock  as  closely 
resembhng  black-rot,  except  that  it  is  more  watery.  Often, 
too,  the  petioles  rot  away 
at  the  base  and  the  leaves 
droop.  The  general  prac- 
tices recommended  under 
lettuce  drop  will  apply. 

Downy-mildew  (Pe)-- 
onospora  'parasitica  (Pers.) 
De  Bary).  —  Downy-mil- 
dew produces  the  char- 
acteristic downy  patches 
of  sporophores  upon  the 
lower  surface  of  the  leaves, 
much  as  is  the  case  of  the 
grape.  Seen  from  above 
the  diseased  spots  are  an- 
gular, limited  by  the  veins, 
pale  yellow,  and  the  tissue 
is  somewhat  shrunken. 

The  disease  is  common 
to  cabbage,  collard,  cauli- 
flower, turnip,  radish,  and 
many  other  members  of 
the  cress  family.  It  has 
been  reported  in  several 
states,  notably  Ohio,  New  Jerse}^  New  York,  Delaware, 
Maryland,  South  Carolina,  North  Carolina,  West  Virginia, 
and  in  Europe  and  Australia.  Though  it  is  seldom  of  impor- 
tance in  the  field,  it  occasionally  does  damage  in  the  seed  bed. 

Spraying  the  plants  in  the  seed  bed  with  Bordeaux  mix- 
ture will  hold  the  disease  in  check.  Diseased  plants  should 
be  destroyed  by  fire  as  soon  as  the  bed  has  been  used. 


Fig.  93.  — ■  Seedling  cabl)age  plant 
spotted  with  downy-mildew. 
Original. 


172  Diseases  of  Economic  Plants 

Yellows,  Wilt  '-'"^'  -'^'  -'-■'  (Fusarium  conglutinans  Woll.).  — 
This  wilt  of  cabbage  is  destructive  through  a  large  territory, 
particularly  in  the  Southern  states,  and  at  least  as  far 
north  as  Minnesota.  As  high  as  90  per  cent  of  loss  has 
been  reported. 

The  chief  symptom  is  yellowing  and  falling  of  lower  leaves, 
and  eventually  all  of  the  loaves  except  those  of  the  head. 
This  character  may  be  strongly  emphasized  upon  one  side 
of  the  plant  or  even  upon  one  side  of  single  leaves.  Affected 
plants  are  retarded  in  growth  and  often  die.  After  death 
abundant  pink  acervuli  are  seen.  Cross  section  of  an 
affected  stem  shows  the  wood  ring  to  be  darker  than 
normal. 

In  treatment  the  same  methods  should  be  followed  that 
are  suggested  for  cabbage  black-rot;  especially  should  in- 
fested land  be  avoided,  and  the  young  plants  grown  in  healthy 
soil.  The  Volga  and  Houser  are  the  most  resistant  of  the 
older  varieties.  The  Wisconsin  Hollander  is  a  disease  re- 
sistant variety  developed  by  selection. 

White-rust  {Albugo  Candida  (Pers.)  Ktz.).  —  White-rust 
upon  radishes  often  causes  curious  malformation  of  the 
flowers  and  pods,  which  become  overgrown  and  distorted; 
often  a  flower  is  five  times  its  normal  diameter  and  is  color- 
less. Chief  damage  is  thus  done  to  the  seed  crop,  which 
may  be  quite  ruined  by  this  attack  upon  the  flowers.  It  is 
quite  general  on  crucifers,  but  really  injurious  only  to  the 
radish. 

Burning  of  all  infected  trash  is  the  best  preventive. 

Soft-rot  {Bacillus  carotovorus) .  (See  carrot.)  —  This  is  a 
soft,  slimy,  wet  decay  affecting  any  part  of  the  plant,  and 
spreading  rapidly  throughout.  Wounds  are  necessary  to 
infection.  Much  injury  occurs  in  the  field,  but  the  greatest 
loss  is  in  storage  houses.  Here  the  temperature  should  be 
kept  a  degree  or  two  above  freezing,  and  good  ventilation 
secured.  Wounds  should  be  avoided  in  so  far  as  possible, 
and  the  crop  dried  before  storing. 


Vegetable  and  Field  Crops  173 

Minor  diseases 

Malnutrition.-"^  —  Leaves,  yellowish  between  the  veins 
and  at  the  margins,  arc  thickened  and  brittle.  The  cause 
chiefly  rests  in  use  of  too  much  mineral  fertilizer  and  lack  of 
humus. 

Powdery-mildew  (Erysiphe) ;  Damping-off  (various  fungi)  ; 
Ring-spot  (Mycosphcerella)  do  but  small  harm.  Phoma-rot, 
Black-root  (see  beet)  and  a  Macrosporium  leaf-spot  are 
reported  on  the  turnip.  Pale-spot  {Cercosporella  albomacu- 
lans  E.  &  E.)  is  also  common  on  leaves  of  turnips.  An- 
thracnose  '"^•^  (Colletotrichum  higginsianum  Sacc.)  occurs  on 
stems  and  pods  of  turnip,  and  is  especially  injurious  on 
young  plants.  Leaf-spot  -^'^  (Pseudomonas  macidicolum 
McC.)  occurs  on  leaves  of  cauliflower  and  cabbage.  The 
spots  are  brown  to  purplish-gray,  1-3  mm.  in  diameter.  The 
leaves  become  puckered,  and  when  badly  diseased,  fall  off. 

CANTALOUPE.     See  p.  178. 

CAPER 

White-rust  (Albugo)  and  Powdery-mildew  (Erysiphe)  are 
recorded,  but  do  small  harm. 

CARROT 

'  Soft-rot  "^-  -"^  (Bacillus  carotovorus  Jones).  —  In  Vermont 
serious  loss  from  rotting  of  carrots  was  reported  to  the  Exper- 
iment Station  in  1898.  Investigation  by  Jones  showed  it  to 
be  due  to  bacteria  and  that  numerous  other  crops  —  namely, 
turnip,  rutabaga,  radish,  salsify,  parsnip,  onion,  celery, 
hyacinth  leaves,  and  the  fruit  of  tomato,  eggplant,  and 
pepper  —  were  susceptible  to  the  same  disease. 

Rot  begins  in  the  field  and  seriously  increases  during  stor- 
age. The  initial  attack  is  either  at  the  crown  or  root  tip, 
from  which  points  it  proceeds  rapidly  through  the  core, 
which  becomes  softened  and  somewhat  browned  with  a  rather 
sharp  boundary  between  diseased  and  healthy  tissue. 


174 


Diseases  of  Econmnic  Plants 


Fields  known  to  be  inf(^stecl  should  be  relieved  of  sus- 
ceptible crops  by  suitable  rotation.  Manure  which  may 
have  become  infested  in  any  way, 
e.  g.  by  feeding  diseased  crops  to 
stock,  should  be  avoided.  Drying 
of  the  roots  kills  the  causal  or- 
ganism, as  does  also  exposure  to 
sunlight.  Drying  in  the  light  is 
therefore  equivalent  to  surface  dis- 
infection and  serves  to  reduce  the 
damage.  Storage  below  10°  C.  (50° 
F.)  gives  best  results. 

Drop  (Sclcrotinia),  see  lettuce, 
and  Southern-blight  (Sclerotium), 
see  pepper,  are  of  some  im- 
portance. 

CASTOR-BEAN 

Wilt  (Pseudomonas  solanacearum) 
(see  p.  230)  does  considerable  dam- 
age, dwarfing  the  plants,  causing 
typical  wilt,  and  finally  death  of 
many  plants. 

Gray-mold  -'^  (Sclerotinia  ricini, 
Godf.,  Botrytis)  of  flowers,  buds. 
Fig.  94.  —  Carrot  showing  and  pods  in  some  cases  affects  50 
soft-rot;  shaded  portions  to  90  per  cent  of  the  plants  with  a 
represent  the  rotted  part  ^^t  rot.  Diseased  tops  should 
of  the  root.  Redrawn 
after  Jones. 


cut  and  Bordeaux  mixture  used. 


CAULIFLOWER.     See  cabbage. 


CELERY,  PARSLEY,  PARSNIP 

Late-blight  --''  [Septoria  petroselini  Desm.).  —  In  Italy  late- 
l)light  was  first  reported  in  1890;  in  the  United  States  in  1891. 
A  loss  of  1950  carloads  and  a  money  loss  of  $550,000  was 


Vegetable  and  Field  Crops 


175 


estimated  in  California  in  1908;  in  Michigan  in  1915  a  loss  of 
more  than  a  million  dollars.  A  cut  in  price  of  5  to  10  cents 
per  crate  is  common  when  the  bunches  are  only  slightly 
disfigured.  The  disease  occurs  on  celery,  also  on  parsnip  and 
parsley. 

In  its  early  stage  it  consists  of  leaf  spots;  in  later  stages, 
the  infection  of  the  leaf  becomes  general,  numerous  black 
pycnidia  are  scattered  upon  all  parts  and  even  upon  the 


Fig.  95.  —  Celery  leaf  infected  with  Septoria.    After  Coons. 


blanched  petioles.  In  extreme  cases  wilting  of  the  leaves  and 
destruction  of  the  plant  follows.  After  the  celery  is  put  in 
storage  the  disease  may  still  progress  and  do  great  damage, 
rotting  off  the  leaves  and  forcing  early  marketing.  Late- 
blight  is  often  found  in  the  seed  bed,  and  is  probably  carried 
by  the  seed,  since  the  pycnidia  are  abundant  upon  the  seed- 
ing stalks  and  fruit. 

Seeds  should  be  disinfected  and  the  seed  bed  rotated.    If 
the  disease  has  been  troublesome  in  preceding  years,  the 


176  Diseases  of  Economic  Plants 

plants  in  the  seed  bed  should  be  sprayed  with  Bordeaux  mix- 
ture as  soon  as  they  are  above  ground,  and  once  or  twice  a 
week  thereafter  until  transplanted.  If  the  disease  develops 
in  the  field,  the  crop  should  be  sprayed  with  Bordeaux  mix- 
ture at  ten-day  intervals.  The  following  is  taken  from  a 
Michigan  publication  in  1915: 

One-sixth  acre  (from  which  accurate  returns  were 
kept)  sprayed  with  a  knapsack  sprayer  at  a  total  ex- 
pense of  12.00  for  labor  and  material  gave  125  crates 

(10x10)  fine  quality  at  Sl.OO  value $125.00 

A  similar  unsprayed  area  gave  18  crates  poor  quality 

at  50c 9.00 

Excess  return  of  sprayed  plot $116.00 

Cost  of  spraying 2 .  00 


Net  gain $114.00 

On  the  rest  of  the  acreage,  at  an  expense  of  not  more  than 
$12.00,  Mr.  Joldersma  saved  a  crop  valued  at  about  $1500. 

To  minimize  loss  no  diseased  plants  should  be  stored.  If 
storage  is  imperative,  badly  infested  leaves  should  be  picked 
off,  and  in  extreme  cases  the  plants  should  be  dipped  in  a 
fungicide  (ammoniacal  copper  carbonate)  before  they  are 
stored  away. 

Early-blight,  leaf-spot,  ^^^  (Cercospora  apii  Fr.).  —  Leaf- 
spot  is  common  on  celery,  parsley,  and  parsnip  in  both 
Europe  and  America.  It  is  reported  from  California  to  New 
Jersey.  In  Florida  in  1906  it  is  said  to  have  injured  80  per 
cent  of  the  crop.  The  crop  is  largely  reduced,  and  the  un- 
sightliness  of  the  spots  injures  the  sala])ility  of  the  product. 

The  spots  appear  first  upon  the  outer,  older  leaves  as 
pale  yellowish  areas,  showing  from  both  sides  of  the  leaf. 
They  are  irregular  with  slightly  raised  border  and  are  an- 
gular in  outline,  owing  to  their  limitat  ion  by  the  veins.  They 
seldom  exceed  3-()  mm.  in  diameter  imloss  by  the  coalescence 


Vegetable  and  Field  Crops  177 

of  several  spots.  The  spots  soon  become  brown,  and  the 
central  part  turns  ashen-white  and  is  seen  by  the  aid  of  a 
hand  lens  to  bear  numerous  hyphge.  The  leaves  may  bear  so 
many  spots  as  to  appear  as  though  scorched,  and  often  death 
results  to  the  entire  plant. 

The  disease  spreads  most  rapidly  in  damp,  warm  weather. 

Market!  difference  in  varietal  resistance  was  reported  by 


Fig.  96.  —  Early-blight  of  celery.    Original. 

Tracy  as  early  as  1885,  the  Boston  Market  and  Golden 
Heart  suffering  much,  while  the  White  Plume  was  but  slightly 
injured. 

All  plants  showing  a  trace  of  disease  should  be  rejected. 
Healthy  plants  from  infected  lots  may  with  advantage  be 
dipped  in  Bordeaux  mixture  to  cleanse  them  of  adhering 
spores.  Spraying  with  ammoniacal  copper  carbonate  or 
Bordeaux  mixture  is  effective.  Treatment  should  be  begun 
before  the  disease  appears,  i.  e.,  in  the  seed  bed,  and  con- 


178  Diseases  of  Economic  Plants 

tinued  at  ten-day  to  fourteen-day  intervals  throughout  the 
growing  period.    All  spore-bearing  refuse  should  be  burned. 

Minor  diseases 

Leaf -spot  (Phyllosticta  apii  Halst.). — -A  dull  brown,  cir- 
cular pycnidia-bearing  patch,  not  to  be  confused  with  the 
light,  ashen-colored,  angular  Cercospora  spot,  is  charac- 
teristic. Soft-rot  (Bacillus  carotovorus)  consists  of  a  soft, 
light-brown  rot  of  the  central  bud,  sometimes  of  the  leaf 
or  leaf  stalks.  It  occurs  on  celery,  also  on  parsley,  and 
is  probably  identical  with  the  carrot  soft-rot.  Rust  {Puc- 
cinia  bullata  (Pers.)  Wint.)  has  not  yet  been  destructive  in 
America.  Damping-ofif  due  to  Sclerotinia,  Rhizoctonia,  and 
Fusarium  have  caused  much  loss  in  the  South  on  both  celery 
and  parsley.  See  also  p.  19.  Pithiness. -^'^ — The  stalks  and 
hearts  are  pithy,  a  condition  attributed  to  the  parent  plant 
and  heredity,  not  to  parasites  or  environment.  As  high  as 
30  per  cent  of  pithy  plants  have  resulted  from  certain  lots  of 
seed.  Proper  rogueing  of  seed  plants  is  recommended.  Scab 
due  to  Phoma  apiicola  Kleb.  consists  of  rotting  of  the  roots, 
leaving  the  plant  with  a  conical  rotten  base. 

CHARD.     See  beet. 

CHIVE.     See  onion. 

COLLARD.     See  cabbage. 

CUCURBITS:    CUCUMBER,  ^^s  MUSKMELON,    MELONS, 

WATERMELON,  PUMPKIN,  SQUASH 

Downy-mildew  ^^^  (Peronoplasmopara  cubensis  (B.  &  C.) 
Clint.). —  Downy-mildew  first  shows  its  presence  by  yellowish 
angular  spots,  3-6  mm.  in  diameter,  upon  the  leaves  as  seen 
from  above.  These  appear  first  upon  the  older  leaves  at 
the  center  of  the  plant.  The  spots  become  more  distinct, 
enlarge,  increase  in  number,  and  soon  the  whole  leaf  be- 
comes pale,  sickly,  and  dies.     If  the  weather  is  moist,  the 


Vegetable  and  Field  Crops 


179 


characteristic  white  hyphse  and  spores  tinged  with  purple 
may  be  seen  on  the  under  sides  of  the  older  spots.  The 
disease  progresses  to  the  younger  leaves,  slowly  in  dry  or 
cool  weather,  but  very  rapidly  in  warm,  wet  weather.  The 
field  is  soon  reduced  to  a  mass  of  dry,  dead  leaves. 


Fig.  97.  —  Spots  of  downy-mildew  upon  cucumber  leaf.     After  Orton. 

The  mildew  was  first  described  in  1868  from  Cuba.  In 
1889  it  attracted  attention  in  the  United  States  (New  Jersey, 
Florida,  and  Texas)  and  in  Japan.  Since  that  time  it  has 
been  destructive  in  many  states.  The  loss  in  Wayne  County, 
Ohio,  alone  was  estimated  at  $45,000  in  one  season. 

It  grows  upon  muskmelons  and  cucumbers  in  most  de- 
structive form  and  is  less  injurious  to  squash,    pumpkin, 


180 


Diseases  of  Economic  Plants 


watermelon,  gourd,  and  other  cucurbits.  The  fungus  winters 
out  of  doors  in  the  South  and  in  the  greenhouse  in  the  North 
and  spreads  thence  to  the  fields  annually  if  weather  condi- 
tions are  favorable. 

This  disease  is  often  injurious  to  cucumbers  under  glass 

as  well  as  in  the  field. 


It  is  well  to  sulfur 
the  greenhouses 
thoroughly  when  not 
in  use  and  to  clean 
and  whitewash  all 
walls  and  wood  in 
order  to  kill  any  fungi 
present.  Should  the 
disease  appear,  spray 
at  once  as  in  field 
pi-actice.  For  direc- 
tion for  field  spraying 
sec  cucurbit  spray- 
ing, p.  191. 

Anthracnose  -^-*  -^'^' 
^^-  {Colletotrichum  la- 
genm'ium  (Pers.)  E. 
&  H.).  —  This  disease 
was  first  noted  in 
1867  in  Italy,  and 
is  now  common  in 
Europe  and  the 
United  States,  occur- 
ring on  cucumber, 
muskmelon,  water- 
melon, gourd,  and  a 
few  other  related  plants.  The  loss  is  severe  on  the  three  crops 
first  named,  and  is  of  more  importance  to  cold-frame  crops 
and  crops  under  glass  than  to  field  crops,  though  it  some- 
times does  cause  almost  total  loss  of  the  latter.  Upon  the 
leaf,  circular,  not  angular,  spots  occur  which,  instead  of 


Fig.  98.  —  Portion  of  watermelon  showing 
effect  of  anthracnose.    After  Sheldon. 


Vegetable  and  Field  Crops  181 

yellowing,  turn  brown,  die,  and  become  ragged  in  appear- 
ance. Tendrils,  buds,  and  petioles  turn  black  and  die.  Upon 
the  stems  and  fruit  the  spots  are  sunken  and  bear  numerous 
acervuli.  Its  most  conspicuous  form  is  upon  the  fruit  at  any 
age,  especially  at  maturity.  Here  very  characteristic  sunken 
spots  with  pink  centers,  much  like  the  bean  pod-spot,  are 
produced.  Upon  old  melons  they  do  but  slight  injury,  but  to 
young  fruit  the  attack  is  often  fatal.  A  bitter  taste  is  often 
imparted  to  the  fruit.  The  disease  is  spread  through  the 
field  by  rain  and  surface  drainage  water,  and  winters  in  the 
field.    It  is  probably  carried  to  new  fields  by  the  seed. 

Spraying  with  4-4-50  Bordeaux  mixture  is  recommended. 
Clean  seed  should  be  used,  or  the  seed  disinfected.  It  is  also 
well  to  destroy  infective  refuse  and  to  practice  rotation. 

Wilt  '-^^  {Fusarium  vasinfectum  Atk.)  —  The  melon  wilt 
not  only  destroys  the  growing  crop,  but  prevents  the  suc- 
cessful culture  of  melons  upon  the  field  in  question  in  suc- 
ceeding years.  It  is  less  frequently  met  on  the  muskmelon 
than  on  watermelons.  A  similar  wilt  of  squash  is  said  to 
be  caused  by  a  different  Fusarium.  The  wilt  has  spread, 
rapidly  during  the  past  decade,  and  is  now  known  from  the 
Atlantic  to  the  Pacific,  and  from  the  Gulf  to  Iowa. 

The  first  symptom  appears  in  the  leaves  which  droop  as 
though  they  were  suffering  from  want  of  moisture.  The 
leaves  and  runners  wilt  rapidly,  and  this  is  soon  followed  by 
the  death  of  the  entire  plant. 

Upon  cutting  the  main  tap  root  across  near  the  surface 
of  the  ground,  the  wood  presents  a  yellow  color,  making  a 
distinct  contrast  with  the  white  wood  of  the  healthy  plants. 
This  one  character,  taken  together  with  the  wilted  appear- 
ance of  the  vine,  enables  recognition  of  the  true  wilt.  The 
further  fact  that  a  field  once  infested  shows  the  same  disease 
in  succeeding  years  in  the  same  or  in  extended  areas  is  an 
additional  recognition  mark. 

Its  spread  may  occur  in  the  ways  mentioned  under  soil 
diseases  and  in  particular  through  the  use  of  infested  manure. 

To  restrict  it  to  its  present  confines,  crop  rotation  should 


182  Diseases  of  Economic  Plants 

be  practiced  and  infested  soil  should  not  be  replanted  to 
melons  until  the  wilt  fungus  is  largely  diminished  in  quantity. 
This  will  probably  take  more  than  four  years,  possibly  eight 
or  ten  years,  and  even  at  the  end  of  that  time  it  is  best  to 
try  a  few  hills  before  planting  the  whole  field  to  melons. 
Cattle  should  not  be  allowed  to  pasture  upon  diseased  vines 
and  thus  spread  the  wilt  through  manure. 

The  practice  of  raising  cowpeas  after  melons  leads  to  the 
presence  of  some  melon  vines  in  the  cowpea  hay,  and  this 
likewise  leads  to  the  presence  of  the  causal  fungus  in  the 
compost  heap.  Manure  so  exposed  to  infestation  should  never 
be  placed  on  land  which  is  still  free  from  the  germ,  or  which 
is  to  be  used  for  melon  culture,  since  this  is  certain  to  spread 
the  wilt. 

There  is  no  objection  to  the  use  of  stable  manure  which 
does  not  contain  the  fungus,  but  experience  has  shown 
that  when  the  wilt  once  gains  entrance  to  the  compost  heap 
or  barnyard,  it  remains  there  for  years,  and  all  of  the  manure 
taken  out  of  such  a  yard  is  likely  to  spread  the  disease.  Hence 
it  is  exceedingly  dangerous,  in  regions  where  the  wilt  pre- 
vails, to  use  any  stable  manure  on  the  field  where  melons  are 
to  be  planted. 

Varieties  resistant  to  this  disease  have  been  developed  by 
the  United  States  Department  of  Agriculture  by  crossing  the 
citron,  which  possesses  high  resistance,  with  the  watermelon, 
and  then  by  practicing  selection  to  attain  the  desired 
edibility. 

Wilt^^o-  '^^o  (Bacillus  tmcheijMlus  EFS.).  — The  cucum- 
ber, muskmelon,  pumpkin  and  squash  are  susceptible  but 
not  the  watermelon. 

The  disease  has  been  reported  from  many  states  —  among 
them  Nebraska,  Wisconsin,  Maryland,  Massachusetts, 
Indiana  — ■  and  is  presumably  present  in  many  others. 

The  attack  in  first  stages  causes  the  vine  to  droop  through- 
out its  length.  This  is  followed  l)}--  death.  The  infection  is 
spread  by  insects,  particularly  beetles  on  which  the  bacteria 
probably  hibernate  to  some  extent. 


Vegetable  and  Field  Crops  183 

Spraying  with  strong  Bordeaux  mixture,  4-5-50,  with 
two  pounds  of  lead  arsenate  powder  added  is  recommended. 
Diseased  vines  should  be  pulled  and  burned,  rotation  prac- 
ticed, and  in  general  the  suggestions  given  under  soil  dis- 
eases (p.  26)  should  be  followed. 

Timber-rot  '"^^  {Sdcrotinia  libertiana  Fcl.).  —  Upon  cucum- 
l^ers  and  other  cucurbits  under  glass  this  disease  occasions 
serious  loss.  It  is  rare  out-of-doors.  The  first  indication 
is  the  appearance  of  a  dense  mass  of  white  mycelium  near 
the  nodes  of  the  stem  which  is  still  green.  As  the  disease 
progresses  the  stem  shrinks  and  yellows,  the  softer  parts 
decay,  and  the  stem  finally  dries  up.  In  the  interior  of  af- 
fected stems  the  white  mycelium,  and  later  near  the  nodes 
or  in  the  external  mycelial  masses,  smooth,  slender,  black 
sclerotia  may  be  found.  The  germination  of  the  sclerotia, 
described  under  lettuce  drop  (p.  197)  results  in  immense 
numbers  of  spores.  These  falling  upon  dead  tissues  germinate 
and  form  a  mycelium  which  attains  such  vigor  as  to  enable  it 
to  attack  healthy  tissue  and  rapidly  destroy  it. 

To  control  this  disease  all  infected  plants  should  be  de- 
stroyed by  fire  before  they  have  had  opportunity  to  form 
sclerotia,  and  the  places  from  which  they  are  taken  should 
be  sprayed  with  a  heavy  application  of  some  fungicide. 

Leaf-blight  -^''  (Alternaria  hrassicce  (Berk.)  Sacc.  var. 
nigrescens  Pegl.).  —  Leaf -blight  and  downy-mildew  are  the 
most  destructive  diseases  of  the  muskmelon  in  this  country. 
In  Florida,  in  some  seasons,  nearly  the  whole  commercial 
crop  is  lost.  Much  damage  has  been  reported  from  Ohio, 
Indiana,  and  Colorado. 

Leaf-blight  begins  as  small,  round,  brown  spots  usually 
marked  by  concentric  rings.  In  the  centers  of  these  spots 
the  hyphse  develop  a  moldlike  growth.  The  spots  enlarge, 
to  a  centimeter  or  more,  coalesce,  dry,  and  cause  the  leaf  to 
curl  and  shrivel  at  the  margin.  The  petioles  and  veins  are 
also  affected.  Ripening  of  the  melons  is  hastened,  but  the 
quality  is  destroyed,  the  fruit  becoming  soft,  wilted,  insipid, 
and  valueless. 


184 


Diseases  of  Economic  Plants 


Fig.  99.  —  The  Pollock  muskincluu  vines  udjacciit  to  those  shown 
in  Fig.  100,  showing  complete  resistance  to  the  leaf-blight. 
After  Blinn. 


Fig.  100.  —  Muskmelon  showing  complete  death  of  vines  attacked 
by  leaf-blight.    After  Blinn. 


Vegetable  and  Field  Crops 


185 


If  melons  be  repeatedly  grown  upon  the  same  field,  the 
disease  increases  year  by  year;  hence  rotation  should  be 
practiced,  and  resistant  varieties  should  be  used.  A  promis- 
ing resistant  variety  has  been  reported  by  Blinn.  Spraying 
as  recommended  for  cucurbits  generally  is  effective. 

Southern-blight  {Sderotium  rolfsii  Sacc).  —  A  large  per- 
centage of   the  muskmelon  and  watermelon  crops  in   the 


Fig.  101.  —  Muskmelon  leaf  spotted  with  downy-mildew. 
Original. 

southernmost  states  is  often  destroyed  by  this  disease.  It  is 
particularly  noticeable  on  fruit  upon  the  side  touching  the 
ground,  first  as  a  slight  rot  (ground-rot),  followed  by  a  white 
fringe  of  fungous  threads  which  soon  surround  the  whole 
fruit.  Later  sclerotia  appear  as  smaU  round  bodies,  dirty 
white  to  dark  brown.  For  further  description  and  treatment, 
see  pepper. 

Angular  leaf-spot  ^^^'  ^^^'  '^^  (Pseudomonas  lachrymans  (S. 
&  B.).  —  This  disease  is  now  known  in  many  of  the  eastern 


Diseases  of  Economic  Plants 


and  middle  states,  and  causes  large  loss.  Affected  fruits  rot 
into  a  soft,  slimy,  wet  mass,  this  occurring  often  in  transit. 
On  the  leaves  dark,  watery  spots,  3-5  mm.  in  diameter,  ap- 
pear. The  spots  later  l^ecome  dry  and  brown,  and  the 
brittle  tissue  usually  falls  away,  leaving  a  ragged,  irregular 

hole.  Spots  on  the 
fruit  are  at  first  small, 
2-3  mm.,  and  watery, 
and  exude  a  gummy 
liquid  which  later  dries 
to  a  white  residue. 
Infection  proceeds  to 
the  interior,  and  in  a 
few  days  the  central 
portion  becomes  a 
rotten  mass.  Young 
fruits  are  especially 
susceptible.  Care 
should  be  taken  in 
picking  to  avoid 
wounding  the  fruit, 
and  all  affected  fruits 
should  be  most  scrupu- 
lously sorted  out  of 
lots  that  are  for  ship- 
ment. The  season's 
infection  may  originate 
either    from    diseased 


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H 

^n/Blt^Kmi  -* 

/^BHB 

/ 

i 

-  Jr 

Fig.  102.  —  Sclerotium  rolfsii  Sacc.  grow- 
ing upon  a  muskmelon  at  point  of  con- 
tact with  the  soil.     After  Hume, 


seed  or  from  soil.     The  use  of  seeds  treated  with  mercuric 
chlorid  reduces  infection. 

Mosaic.  '-'^'^'  -^^  —  Two  mosaic  diseases  of  cucurbits  are: 
the  White-pickle-mosaic,  which  affects  many  hosts,  and  the 
Mottled-leaf-mosaic,  common  to  only  a  few  hosts.  The 
status  of  knowledge  is  much  as  in  the  case  of  other  mosaics. 
See  p.  258.  Inoculations  are  readily  made  by  rubbing.  In 
the  field,  infection  is  carried  by  beetles  and  by  the  pickers. 
Experiments  have  shown  18  species  in  10  genera  of  cucurbits 


Vegetable  and  Field  Crops  187 

to  be  susceptible,  but  the  disease  is  not  identical  with  those  of 
bean,  tobacco,  tomato.  Mosaic  is  regarded  as  the  most 
serious  disease  of  the  cucumber  in  the  Middle  West,  and  it 
ranges  from  California  to  Virginia  and  Texas.  Mosaic  on 
squash  and  pumpkin  appears  to  be  a  distinct  disease. 

Powdery-mildew  -•^■^  {Erysiphe  polygoni  DC). — ^This  mil- 
dew on  cucurbits  generally  has  the  common  characteristics 
of  the  powdery-mildews,  a  whitish  flourlike  coating  upon  the 
leaves  and  stems;  at  first  in  circular  spots,  but  later  diffuse. 
Its  presence  on  cucumbers  in  America  was  first  announced 
by  Humphrey.  It  has  since  frequently  been  observed  in  the 
field  and  occasionally  under  glass. 

The  fungus  appears  chiefly  upon  the  upper  leaf  surfaces 
and  is  most  developed  upon  the  older  leaves.  It  renders  the 
fruits  bitter  and  distorts  them.  If  it  occurs  in  the  greenhouse, 
flowers  of  sulfur  applied  to  the  hot  water  or  steam  pipes  in  the 
form  of  a  i:)aste  is  useful. 

Stem-end-rot -''^  {Diplodia  sp.).- — In  transit  watermelons 
often  shrivel  and  develop  a  wet,  slimy  rot,  which  may  progress 
lJ/2  inches  in  a  day.  Many  cars  reach  their  destination  with 
75  to  95  per  cent  of  their  contents  spoiled.  In  one  day  100 
cars  showed  an  average  of  25  per  cent  loss.  Diseased  refuse 
should  be  destroyed,  clean  culture  and  deep  plowing  practiced, 
and  cutters  in  harvesting  must  avoid  spreading  the  contagion. 
It  is  recommended  that  the  freshly  cut  stem-end  be  coated 
with  an  antiseptic  paste;  hot  water,  3)^  qts.,  copper  sulfate, 
8  oz.;  add  to  starch  paste,  4  oz.  to  1  pt.  of  cold  water. 

Leaf-blight,  fruit-spot  "^^  (Cladosporium  cucumerinum  E. 
&  A.) .  —  This  spotting  on  cucumbers  was  first  noted  at 
Geneva,  N.  Y.,  in  1887,  where  it  was  so  abundant  as  to 
ruin  the  pickle  crop.    It  is  occasional  on  melons. 

The  spots  begin,  when  the  fruit  is  only  2-5  cm.  long,  as  gray, 
slightly  sunken  areas  with  delicate,  velvety  surfaces.  They 
are  about  3  mm.  in  diameter,  but  coalesce  into  irregular 
patches,  particularly  toward  the  flower  end.  As  the  spots 
age  they  darken  to  greenish  black,  and  a  gummy  exudate 
often  appears. 


188 


Diseases  of  Economic  Plants 


Upon  leaves,  where  injury  is  less  common  than  upon  the 
fruit,  the  spots  are  at  first  watery  and  translucent;  later 
the  leaf  wilts,  and  is  soon  reduced  to  a  decayed  mass.  The 
disease  progresses  so  fast  that  a  plant  may  be  practically 


Fig.  103.  —  Part  of  waterinelon  with  .stein-end-rot.    After  i\Ici( 


destroyed  in  a  few  days.  Immediate  and  thorough  spray- 
ing may  be  of  service. 
■  Soft-rot  218' 219  {Bacillus  melonis  Gidd.).  — This  soft-rot 
was  described  first  by  Giddings  as  causing  25  per  cent  loss  of 
muskmelons  in  certain  fields  in  Vermont  in  1907.  The  decay 
usually  Ijegins  on  the  lower  side  of  the  fruit,  resulting  in 


Vegetable  and  Field  Crops 


189 


shrunken,  diseased  areas  over  which  the  skin  remains  un- 
broken. The  flesh  near  the  point  of  infection  becomes  com- 
pletely decayed  and  has  an  offensive  odor. 


Fig.  104.  —  Muskmelon  65  hours  after  inoculation  with 
Giddings'  germ.     After  Giddings. 


The  cause  is  a  bacillus  whicli  gains  entrance  through 
wounds,  often  through  ruptures  occasioned  by  excessively 
rapid  growth. 


190 


Diseases  of  Economic  Plants 


Spraying  with  Bordeaux  mixture  is  recommended;  also 

turning  the  melons  so  as  to  expose  all  sides  to  light  and  air. 

Wilt  ^-°  (Mijcosphcerella  citndlina  (Sm.)  Gr.,  Diplodina).  — 

This  wilt  or  canker  seems  to  be  rare,  perhaps  affecting  to 

serious  extent  greenhouse-grown 

muskmelons;   only   occasionally 

field     muskmelons     and     other 

cucurbits. 

Infection  is  local  at  the  nodes 
in  the  leaf  axil,  never  at  inter- 
nodes.  The  edges  of  the  infected 
areas  are  "oily  green"  in  color, 
often  with  resin-colored,  gummy 
exudate.  The  older  parts  are 
either  dark  and  gummy,  or  dry 
and  gray,  and  bear  many  brown 
pycnidia. 

Spraying  with  Bordeaux  mix- 
ture after  the  plants  are  about 
half  grown,  but  before  the  dis- 
ease appears,  and  often  enough 
thereafter  to  cover  growing 
parts,  is  recommended. 

Minor  diseases 

Leaf-spot  (Phyllosticta  cucur- 
hitacearumSacc.)  on  muskmelons 
has  been  destructive  in  several 
states,  notably  so  in  New  Jer- 
sey and  Ohio.  The  spots  are 
light-colored  and  pycnidia  ap- 
pear in  their  centers. 
A  Leaf-spot  *^^^  (Stemphylium  cucurbitacearum  Osn.),  3-4 
mm.  in  diameter,  circular  or  irregular  in  outline,  visible  from 
both  sides  of  the  leaf,  with  centers  yellow-brown  and  red 
bordered,  is  reported  from  Indiana  and  Ohio  as  causing 
some  loss. 


Fig.  105.  — •  Portions  of  musk- 
melon  vine  showing  pycni- 
dia and  perithecia  of  Myco- 
sphserella.   After  Dorsey. 


Vegetable  and  Field  Crops  191 

Two  Cercospora  leaf-spots  also  occur  on  cucumber  and 
watermelon,  and  two  Septoria  leaf-spots  on  cucurlnts  gen- 
erally. 

Leaf -glaze -^^  {Acremonium  sp.).  —  Shoots  are  stunted, 
fruits  deformed,  and  leaves  yellowed  and  killed.  Upon  the 
lower  leaf  surfaces  a  delicate  white,  glossy  film  like  dried 
albumen  is  seen.  Plants  that  are  attacked  ma}^  put  forth 
new,  vigorous  shoots  to  survive  for  a  time;,  then  die.  The 
disease  has  been  known  to  reduce  the  jaeld  90  per  cent.  No 
treatment  has  been  advocated. 

Blossom-rot  (Rhizopus  nigricans  Ehr.,  Choanephora  cucur- 
hitarum  (B.  &  Rav.)  Thaxt.)  spreads  to  the  young  squash, 
cucumber,  or  pumpkin,  causing  loss  of  the  fruit  })y  soft- 
rot. 

Root-knot  (nematodes).  Of  the  cucurliits,  the  watermelon 
is  very  susceptible.  Root-rot  due  to  Thielavia  is  somewhat 
injurious. 

Cucurbit  Spraying  -^'* 

Planting  should  be  at  such  distance  as  to  facilitate  ma- 
chine spraying;  that  is,  relatively  close  in  the  row,  but  with 
the  rows  wider  apart  than  is  usual  in  most  sections  of  the 
country.  In  cultivating,  the  vines  should  be  induced  to 
spread  along  the  row,  and  by  the  use  of  a  vine  turner  a 
one-foot  open  alley  may  be  maintained  throughout  the  season 
for  the  wheels  of  the  sprayer. 

By  means  of  a  geared  sprayer  with  proper  length  of  axle 
to  cover  one  row,  three  rows  may  be  sprayed  at  one  time. 
Particular  attention  must  be  given  to  reaching  the  under  sides 
of  the  leaves  with  the  spray.  Spray  first  when  the  vines  begin 
to  run,  using  3-6-50  Bordeaux  mixture.  For  subsequent 
sprayings  use  4-4-50  Bordeaux  mixture  at  intervals  of  about 
ten  days  if  the  weather  is  drj^;  oft  oner,  if  growth  is  rapid. 
The  net  profits  from  this  treatment  have  been  as  high  as 
$163.50  an  acre. 


192  Diseases  of  Economic  Plants 

EGGPLANT  ^^3 

Wilt   {Pseudomonas  solanacearum) .     See  tobacco. 

Wilt  {Nectria  i-pomoece  Hals.). — -Fields  have  been  so 
attacked  that  scarcely  a  fruit  was  gathered.  The  affected 
plants  when  half  grown  take  on  a  yellowish,  sickly  appear- 
ance, the  foliage  wilts,  the  lower  part  of  the  stem  becomes 
coated  with  a  whitish  mold,  and  the  plant  usually  dies. 
Numerous  small,  pink  perithecia  are  found  upon  the  stem 
just  below,  or  at  the  surface  of  the  ground. 

This  disease  is  close  kin  to  the  wilt  of  cotton,  and  what 
is  said  in  that  connection  regarding  treatment,  applies  here. 

Another  wilt  due  to  a  CoUetotrichum  is  reported  as  the 
cause  of  large  loss  in  Utah.  A  similar  wilt  due  to  Verticillium 
is  also  reported. 

Leaf-spot  {Phomo-psis  vexans  (Sacc.  &  Syd.)  Hart.).  — 
Plants  in  the  hotbed  are  subject  to  leaf-spot  attack,  the 
transplants  dying,  or  it  may  appear  later  upon  leaves  and 
fruit,  and  result  in  more  or  less  serious  leaf  injury. 

Upon  the  leaf,  large,  irregular,  brown  or  gray  patches  are 
produced.  Here  numerous  black  pycnidia  appear,  and  later 
the  leaf  becomes  torn.  Upon  the  fruit  the  spots  are  at  first 
soft  and  watery,  but  later  become  dry  and  leathery. 

Treatment  with  Bordeaux  mixture  or  ammoniacal  cop- 
per carbonate  before  transplanting  is  recommended,  fol- 
lowed by  similar  spraying  in  the  field.  Eight  sprayings 
with  Bordeaux  mixture  in  one  test  yielded  100  fruits,  while 
a  similar  plat,  unsprayed,  gave  only  about  half  as  many. 
Clean  culture  should  be  followed. 

Gray-mold  {Botrytis  fascicular  is  (Cda.)  Sacc).  —  In  this 
rot  the  purple  fruits  show  tan-colored  blotches,  followed 
by  softening  of  the  tissue  and  rapid  development  of  a  gray 
mold,  the  fruit  in  the  meantime  changing  into  a  completely 
rotten  mass. 

Minor  diseases 

Anthracnose  {Gloeosporium  melongence  E.  &  H.).  —  Pits 
appear  upon  the  fruits,  and  in  these  the  pink-tinted  acervuli. 


Vegetable  and  Field  Crops  193 

Blue-mold  {Penicillium  sp.)  is  very  similar  to  blue-mold  on 
apples.  Damping-off  {Pythium  deharyanum) . — See  p.  19. 
Southern-blight  (Sderotium)  is  common  in  the  South;  Cor- 
ticium  docs  some  injury  to  roots  and  causes  occasional  fruit 
rot;  Root-knot  due  to  nematodes  is  common  as  is  also  Drop 
{Sderotima  libcrtiana) . 

GARLIC.    See  onion. 


GINSENG  2«-246 

Blight  {AUernaria  panax  Whet.).  —  Brown  cankers  upon 
the  stem,  and  watery  spots  in  the  leaf,  often  involving  the 
entire  top  of  the  plant,  mark  this  disease.  Badly  blighted 
plants  appear  as  if  drenched  with  boiling  water.  It  is  a 
serious  menace  to  the  ginseng  industry  of  New  York  state. 
The  seed  crop  is  sometimes  completely  lost. 

It  can  be  controlled  by  thorough  spraying  with  3-3-50 
Bordeaux  mixture  as  soon  as  the  plants  come  up,  repeated 
every  other  day  during  the  first  few  weeks,  less  often  later. 
Diseased  refuse  should  be  destroyed. 

Wilt  {Fusarium  vasinfedwn  Atk.).  — ■  With  the  first  symp- 
tom of  attack  the  leaflets  droop,  yellow,  and  die;  then  the 
entire  leaf  dies  to  the  base,  dries  up,  and  falls  off.  The 
immature  seeds  shrivel  and  fail  to  mature.  Secondary 
decays,  soft  rots,  may  follow. 

Methods  of  control  suggested  for  watermelon  wilt  apply 
here  also. 

Stem  anthracnose  {Vermiculaj-ia  de^natium  (Pers.)  Fr.).  — 
Numerous  black  scars  appear  on  the  stems  a  few  weeks 
after  the  plants  come  above  ground.  These  spread  and 
sometimes  encircle  the  stems.  The  leaflets  then  brown. 
Often  the  plants  fall  over,  even  before  they  wilt.  The  great- 
est loss  lies  in  the  destruction  of  the  seed  crop. 

Bordeaux  mixture  applied  about  three  weeks  after  the 
plants  appear  in  the  spring  and  each  three  weeks  thereafter, 
until  August,  more  often  if  the  season  is  wet,  will  control 


194  Diseases  of  Economic  Plants 

the  disease.  All  dead  stalks,  leaves,  etc.,  should  be  collected 
and  burned  in  the  fall. 

Verticillium  wilt  {V erticiUium  albus  (Preuss)).  —  This  wilt 
is  due  to  stoppage  of  the  veins  by  fungous  growth,  and  the 
chief  symptom  is  wilting  of  the  leaves,  followed  by  death  of 
the  stem  and  leaves.  Sections  of  the  rootstock  reveal  a 
yellowing  of  the  water  ducts  and  veins,  which  contrasts 
strongly  with  the  normal  white  of  a  healthy  plant. 

The  disease  is  largely  confined  to  the  older,  less  vigorous 
roots.  It  is  advisable  to  remove  and  dry  the  infected 
roots  and  to  replace  the  soil  of  infested  beds  with  new, 
healthy  soil.  Soil  disinfection  should  be  employed  if 
practicable. 

Black-rot  (Sclerotima  sviilacina  Dur.).  —  Black,  warty 
sclerotia  upon  the  root  indicate  this  disease.  The  roots  are 
very  black,  but  upon  drying,  bleach  somewhat.  In  old  age 
this  blackening  may  extend  to  the  center  of  the  root,  which 
becomes  wet,  spongy,  and  pliable.  The  disease  remains  in 
the  soil  some  years  after  infestation.  Sick  roots  should  be 
removed  and  burned  if  not  marketable.  Treat  also  as 
for  wilt. 

Soft-rot.  —  This  rot  occurs  widely  and  causes  large  loss. 
The  root  decays  rapidly,  is  sticky  and  ill  smelling.  The 
leaves  turn  red  and  yellow  and  soon  die.  A  rot  ^^''  due  to 
Phytophthora  cactorum  (C.  &  L.)  Schr.  is  reported  as  causing 
a  loss  of  20  per  cent  in  some  beds  in  New  York.  Damping-ofif 
{Corticium)  is  largely  prevented  by  thorough  ventilation,  and 
the  avoidance  of  excess  of  moisture  in  soil  and  air.  Stirring 
the  soil  to  hasten  drying,  aids.  See  p.  19.  Leaf-anthracnose 
{Pestalozzia  funerea,  Desm.)  is  destructive  to  young  plants. 
It  appears  as  a  black,  velvety  growth  at  the  bases  of  the 
leaves  and  flower  stalks,  causing  them  to  die  and  fall  off. 
Spray  as  for  blight.  Thielavia-root-rot  (Thielavia  hasicola) 
is  especially  harmful  to  seedlings,  resulting  in  sudden  wilting, 
which  causes  them  to  bend  over  and  dry  up.  The  fine  roots 
are  affected  as  are  the  roots  of  tolxacco.  Dark  brown,  dry 
lesions  are  also  produced  on  the  roots  by  a  Ramularia. 


Vegetable  and  Field  Crops  195 

Sclerotinia  white-rot  (Sderotinia  Uhertiana)  occurs  to  some 
extent  (see  lettuce).  Root-knot  (nematodes)  and  Southern 
blight  (Sclerotiwn  rolfsii)  are  also  common. 

GOLDENSEAL  (Hydrastis) 

Botrytis-blight.  This  is  the  most  common  and  widely 
distrihutetl  disease  of  this  plant.  Ten  to  20  per  cent  of  the 
tops  are  reported  affected  in  New  York,  Michigan,  and 
Wisconsin. 

Blight  (Alter naria  sp.).  —  Spots  o(;cur  upon  the  leaves. 
The  disease  seems  to  be  identical  with  that  of  ginseng. 

HOP 

Powdery-mildew  {Sphcerothcca  humuli  (DC.)  Burr.). — 
Powdery-mildew,  while  serious  in  many  parts  of  Europe, 
has  been  seen  but  rarely  on  the  hop  in  America,  and  has 
seldom  been  reported  as  seriously  injurious.  It  is  recognized 
by  the  usual  characters  of  the  powdery-mildews.  See  grape. 
If  it  should  become  troublesome,  spraying  with  Bordeaux 
mixture  or  ammoniacal  copper  carbonate  must  be  prac- 
ticed. 

Leaf-spot  {Cylindrosporiu7n  humuli  E.  &  E.).- — Small, 
rusty  brown,  angular  leaf-spots  largely  limited  by  the  veins 
are  present.  They  show  most  clearly  upon  the  lower  sides  of 
the  leaves.  Minute  black  acervuli  are  present.  The  disease 
has  been  reported  from  several  states,  but  has  not  been  re- 
garded as  serious. 

HORSE-RADISH 

Leaf-blight  {Septoria  armor acice  Sacc.  and  Ascochyta  ar- 
moracice  FcL).  —  Ruin  is  occasionally  brought  to  a  crop  by 
these  diseases.  The  leaves  bear  numerous  circular  spots, 
blanched  in  the  center  and  pale  yellow  at  their  borders. 
Pycnidia  are  borne  in  the  centers  of  the  spots.  Badly  affected 
leaves  turn  yellow  and  become  filled  with  holes  caused  by  the 
dropping  of  the  dead  tissue  of  the  spots. 


196  Diseases  of  Economic  Plants 

Leaf-spots  {Ramularia  armoracice  Fcl.  and  Cercospora 
armoracice  Sacc.)-  —  These  spots  are  much  like  those  of  leaf- 
blight  except  that  no  pycnidia  are  present. 

Black-mold  (Macrosporiurn  herculeum  E.  &  M.).  — In 
late  summer  circular,  blanched,  and  later  black,  moldy  leaf- 
spots  are  prevalent.  The  injury  is  not  sufficient  to  warrant 
treatment. 

White-rust  {Albugo  Candida)  and  Downy-mildew  {Peronos- 
pom).  — These  diseases  are  the  same  as  upon  cabbage. 
They  are  often  present  but  usually  insignificant  upon  horse- 
radish.   Root-rot  due  to  Thielavia  also  occurs. 

KA.LE  and  KOHL-RABI.    See  cabbage. 

LETTUCE  251 

Drop -^^  {Sclerotinia  lihertiana  Fcl.).  —  The  outer  lower 
leaves  wilt,  droop,  and  fall  flat  upon  the  ground;  a  similar  fate 
rapidly  overtakes  the  inner  leaves,  and  so  on  over  the  whole 
plant,  until  within  a  few  days  the  entire  plant  is  dead,  lying 
flat  upon  the  ground,  appearing  much  as  though  scalded  by 
hot  water.  The  disease  progresses  with  wonderful  rapidity, 
the  plants  appearing  to  die  in  a  day. 

Upon  the  under  sides  and  at  the  bases  of  the  leaves  occur, 
at  this  time,  dense,  cotton-like  growths  of  mycelium,  and  in 
later  stages,  small,  irregular  black  bodies,  the  sclerotia,  which 
vary  from  3-10  mm.  long,  somewhat  less  in  thickness.  The 
sclerotia  and  the  mycelium  are  unmistakable  signs  of  this 
disease. 

Drop  was  first  definitely  recognized  in  America  in  1900, 
though  it  doubtless  did  much  damage  before  then.  It  has 
since  then  followed  the  rapidly  extending  lettuce  industry 
into  many  states  and  is  particularly  destructive  in  the 
South  Atlantic  seaboard  states  from  Virginia  to  Florida, 
where  its  inroads  upon  the  crop  grown  under  cover  are  es- 
pecially damaging.  The  causal  fungus  may  persist  from 
year  to  year,  as  sclerotia,  in  beds  once  infested  —  beds  cost- 


Vegetable  and  Field  Crops 


197 


ing  originally  often  $1000  per  acre  —  and  thus  destroy  their 
value  for  lettuce  culture.  The  damage  is  thus  much  more 
than  injury  wrought  merely  to  the  current  crop. 

The  sclerotia,  when  favorably  situated,  are  capable  of 
germination,  each  producing  several  trumpet-shaped  organs 
(Fig.  106),  with  stems  about  15  mm.  long  and  disks  3-8  mm. 
or  less  in  diameter.  Spores,  capable  of  initiating  the  fungous 
growth  upon  dead  or  sick  lettuce  tissue,  issue  in  great  num- 
bers from  these  disks,  and  from  material  thus  infested  the 
fungus  can  make  its  way  into  the  healthy  lettuce  plant. 


Fig.  106.  —  Sderotia  of  Sclerotinia  from  lettuce  germinating. 


If  all  infected  plants  be  pulled  and  burned  as  soon  as  the 
first  indication  of  disease  is  observed,  the  formation  of 
sclerotia  will  be  prevented.  As  an  additional  precaution 
it  is  well  to  spray  the  areas  occupied  by  diseased  plants 
thoroughly  with  Bordeaux  mixture  or  bluestone  solution. 

A  few  years  of  such  procedure  will  much  reduce  the  in- 
fection or  perhaps  eliminate  it  entirely.  All  lettuce  trash 
should  be  removed  from  the  beds,  since  it  serves  as  the  ini- 
tial point  of  attack  for  the  fungus.  Growers  whose  land  is 
free  from  the  disease  should  guartl  against  its  introduction 


198  Diseases  of  Economic  Plants 

upon  diseased  refuse  in  any  form.  Compost  which  may  be 
contaminated  with  lettuce  refuse  bearing  this  disease  should 
be  avoided.  Those  growing  lettuce  under  glass  have  found 
soil  disinfection  effective  and  practicable. 

Damping-off.    See  p.  19. 

Gray-mold  {Botrytis  cinerea  Pers.).  —  Gray-mold  is  es- 
sentially a  leaf  disease,  beginning  usually  at  the  leaf  edges, 
and  there  causing  wilted,  flaccid  patches  which  soon  become 
coated  with  a  straw-colored  downy  fuzz,  the  sporiferous 
hyphse.  The  whole  leaf,  ordinarily  an  outer  one,  may  droop 
and  die. 

Weak  plants  may  succumb  entirely  to  such  attack,  the 
disease  passing  slowly  from  the  outer  to  the  inner  leaves. 
In  all  eases  after  the  death  of  the  affected  parts  a  charac- 
teristic, brownish,  fuzzy  coating  appears.  This  disease  may 
be  distinguished  from  drop  by  the  al)sence  of  the  white 
mycelium  and  sclerotia,  and  by  the  presence  of  the  gray 
Botrytis  growth,  which  is  not  a  feature  of  drop.  The  two 
diseases,  while  often  occurring  separate,  may  both  infest  the 
same  beds  or  the  same  plants.  Gray-mold  may  also  cause 
damping-off. 

High  temperature,  lack  of  ventilation,  and  lack  of  vigor  in 
the  plant,  resulting  from  improper  care,  are  conditions  favora- 
ble to  attack  of  gray-mold.  Precaution  with  respect  to 
these  details  is  sufficient  to  insure  against  serious  loss. 

Rosette  (Corticium  vagum). — -A  moist  rot  sets  in,  first 
upon  portions  of  leaves  which  touch  the  ground,  and  spreads 
thence  throughout  the  leaves,  rotting  away  the  blades  but 
leaving  the  midribs  standing,  thus  distinguishing  this  from 
all  other  diseases.  Infection  proceeds  from  leaf  to  leaf  at 
point  of  contact,  often  reaching  the  center  of  the  head, 
while  the  outer  leaves  are  infected  only,  in  spots.  The  inner 
leaves  may  all  ])e  reduced  to  a  slimy  mass  though  the  outer 
leaves  still  remain,  surrounding  it  as  a  rosette. 

Downy-mildew  {Bremia  lactucce  Regel).  —  This  occa- 
sionally destructive  mildew  shows  the  character  of  the 
downy  mildews,  ;".  e.,  downy  fuzz  below,  yellow  spots  above 


Vegetable  and  Field  Crops  199 

(see  grape).  It  is  frequently  reported  as  causing  much  loss  to 
lettuce  under  glass,  especially  upon  the  older  leaves.  It  is 
also  noted  upon  old  leaves  on  seed  plants  of  both  cultivated 
and  wild  lettuce. 

Close  attention  to  proper  cultural  conditions  in  the  green- 
house, especially  as  to  moisture,  ventilation,  and  tempera- 
ture, usually  suffice  to  hold  it  in  check.  Evaporated  sulfur 
also  aids  in  suppressing  the  mildew. 

Bacterial  rots -■^''  (Pseudmnonas  sps.).  —  Several  different 
rots  due  to  bacteria  occur  upon  this  host.  In  some  instances 
the  head  rots  at  the  center,  or  at  the  top.  In  other  cases 
leaves  may  become  spotted  with  large  brown  or  black  areas, 
or  shriveled,  or  give  way  to  a  soft  rot,  or  the  tips  of  the  heart 
leaves  may  die.  In  other  instances,  small  translucent  leaf 
spots  occur;  extending  and  coalescing,  they  occupy  large 
areas,  the  affected  tissues  becoming  diy  and  papery. 

Various  species  of  Pseudomonas,  associated  with  these  rots 
have  been  considered  causal  agents,  but  predisposing  condi- 
tions, as  extreme  cold,  or  other  unfavorable  conditions  of 
temperature,  ventilation,  or  nutriment  seem  to  be  necessary 
to  enable  these  bacteria  to  gain  entrance  into  the  plant: 

Leaf-perforation,  anthracnose  -^^  (Marssonina  panat- 
toniana  (Berl.)  Magn.). — The  most  conspicuous  character 
is  perforation  resulting  from  the  fall  of  the  tissue  killed  by 
the  attacking  fungus.  These  perforations  are  from  1-2  mm., 
or  more,  in  diameter,  with  irregular  borders.  Upon  the 
midrib  and  petiole  depressed  spots  result.  With  small, 
young  leaves  dwarfing  and  distortion  is  produced,  especially 
at  the  apex.  The  disease  appears  to  be  limited  to  green- 
houses and  to  be  spread  largely  by  watering. 

It  was  first  described  by  Selby  in  Ohio  in  1896  and  has 
since  been  noted  in  several  other  states,  ranging  from  the 
Atlantic  to  the  Pacific,  arid  in  Europe.  Diseased  lettuce 
should  be  l)urned.  Watering  by  overhead  systems  leads  to  a 
minimum  of  infection. 

Blight  (Septoria  laducce  Pass,  and  Septoria  condmilis  E.  & 
M.).  —  Upon  the  old,  outer  head-leaves  there  often  appear 


200  Diseases  of  Economic  Plants 

numerous,  black  pycnidia,  so  small  as  to  remain  unnoticed 
unless  by  special  search.  The  injury  is  usually  insignificant, 
though  some  dwarfing  and  curling  of  the  leaf  results.  Upon 
seed  plants  these  same  diseases  attack  the  leaves  with 
greater  vigor,  causing  pale  brown,  discolored  areas  and 
the  death  of  the  older  leaves.  Sometimes,  through  neglect 
to  destroy  plants  of  the  seed  bed,  these  diseases  may  gain 
such  foothold  as  to  cause  injury  in  other  beds.  This  can 
usually  be  avoided  l^y  destruction  of  the  seed-bed  plants  as 
soon  as  transplanting  is  over. 

Root-knot  (nematodes)  occurs  on  lettuce,  doing  some 
damage. 

MANGOLD  a«d  MANGEL  WURZEL.    See  beet. 
MELON.    See  cucumber. 

MUSHROOM 

Mold -•^''  {Mycogone  perniciosa  Magn.). — Though  noted 
in  Germany  as  early  as  1887  this  disease  was  not  called  to 
attention  in  America  until  1909. 

French  experts  detect  the  disease  first  in  the  spawn  as 
an  abnormal,  white,  fluffy  growth.  Later  the  mycelium  of 
the  mushroom  fails  to  develop  normally,  but  instead  pro- 
duces monstrous  soft  growths.  Whole  clumps  develop 
into  moldy  masses,  which  soon  putrify  with  a  clisagreeable 
odor. 

Infested  beds  or  houses  may  be  aliandoned  or  cleaned 
thoroughly,  then  fumigated  with  formalin,  3  pints,  per  1000 
cubic  feet  of  space. 

Bacterial-spotting.-^^  Small  areas,  pale  yellow  to  brown, 
on  cap,  stipe,  or  gills,  or  even  covering  the  whole  plant, 
occur.  Fumigating  the  beds  with  sulfur  before  planting  has 
given  excellent  results. 

MUSKMELON.     See  cucumber. 


Vegetable  and  Field  Crops  201, 

OKRA 

Wilts  ^^^  {Fusariwn  vasmfectwn  Atk.,  Verticillium  alho- 
atrum  R.  &  B.). — Two  wilts  of  okra,  macroscopically  in- 
distinguishable from  each  other,  occur;  both  partake  of  the 
general  character  of  wilts  discussed  elsewhere,  pp.  26,  253. 

Pod-spot  (Ascochyta  abelmoschi  Hart.)  is  reported  from 
New  York  and  Maryland,  and  a  Leaf-spot  {Cercospora)  from 
Porto  Rico.  Texas-root-rot  (Ozonium)  is  injurious  in  the 
Gulf  states. 

ONION,  GARLIC,  CHIVE  ' '' 

Smut  2-^5-257  ^  jjj'ocystis  cepulce  Frost) .  —  As  with  the  wilt  of 
tobacco  and  cotton,  this  fungus  resides  in  the  soil  and  is 
therefore  destructive  not  only  to  the  present  crop,  but  is 
also  prohibitive  of  successful  culture  of  susceptible  crops 
in  the  future. 

The  smut,  which  seems  to  have  originated  upon  a  wild 
variety  of  onion,  occurs  in  both  Europe  and  America.  It 
was  known  in  Connecticut  as  early  as  1860,  Massachusetts, 
Pennsjdvania,  and  Ohio  in  1889,  later  in  New  York,  New 
Jersey,  and  Delaware,  and  has  since  been  recorded  from 
Iowa  and  Georgia.  The  first  mention  of  serious  loss  by 
onion  smut  in  America  was  in  1870.  Its  inroads  upon  the 
crop  are  often  such  as  to  prohibit  profitable  onion  culture 
unless  preventive  measures  are  taken  against  the  disease. 

The  smut  attacks  the  very  young  seedlings  through  the 
still  tender,  delicate  leaf  sheaths.  Onions  grown  from 
sets  are  immune,  and  onions  from  seed,  if  they  pass  the 
very  young  state  without  infection,  are  so  protected  by 
•hardening  of  the  outer  plant  parts  as  to  resist  attack,  even 
if  the  bulb  is  surrounded  l^y  thoroughly  infested  soil. 

Upon  the  infected  seedling  leaves,  dark,  opaque  spots 
may  be  noted,  especially  upon  holding  the  leaves  against 
the  light.  The  portions  of  the  leaf  above  such  spots  soon 
die,  and  the  spots  rupture,  exposing  sooty,  powdery  masses. 
Badly  infected  seedlings  succumb  early,  while  others  may  sur- 


202 


Diseases  of  Econornic  Plants 


vive  until  harvest.    The  disease  is  more?  often  fatal  if  attended 
by  dry  weather,  which  reduces  the  vigor  of  the  host  plant. 


Fig.  107.  —  Young  onion  plants  showing  effect  of  smut. 
At  left,  smutted  plants;  at  right,  healthy  plants  of 
the  same  age.    After  Hinman, 

Plants  surviving  the  disease  show  smut  in  the  outer  leaves, 
often  also  within.     Diseased  bulbs  dry  up  and  rot.     In  han- 
dling they  may  readily  be  distinguished  from  sound  bulbs. 
The  spores  are  liberated  freely  in  the  soil,  where  they 


Vegetable  and  Field  Crops  203 

may  remain  alive  for  many  years.  The  disease  may  be  car- 
ried to  adjacent  fields  by  insects,  also  by  the  means  sug- 
gested under  soil  diseases.  There  is  little  or  no  danger  of 
disease  carriage  by  the  seed. 

Since  onion  sets  are  immune,  the  effects  of  the  smut  can 
be  avoided  by  sowing  seed  in  soil  that  is  free  of  disease  and 
then  transplanting  into  the  field.  With  this  mode  of  onion 
culture  the  only  difficulty  is  to  secure  plats  free  from  in- 
festation, and  this  is  not  often  a  serious  one.  In  extreme 
cases  disinfection  of  the  soil  in  plats  may  be  resorted  to. 
(See  soil  disinfection,  p.  460.)  On  farms  once  infested  all 
refuse  (screenings,  tops  of  infected  sets)  should  be  collected 
and  burned  to  reduce  the  amount  of  spores.  Where  soil, 
known  to  be  infested,  is  to  be  planted,  formalin  (1  ounce  in 
1  gallon  of  water)  should  be  used  and  applied  with  a  drip 
attachment  on  a  seed  drill  in  the  proportion  of  one  gallon 
of  solution  for  each  1200  linear  feet  of  row. 

Ground  quicklime  or  stone  lime,  better  the  former,  ap- 
plied at  the  rate  of  75  to  125  bushels  per  acre  on  the  freshly 
prepared  soil  just  before  seeding,  has  been  useful.  If  ap- 
plied by  drill,  harrowing  will  not  be  required;  if  broadcast, 
harrowing  should  precede  planting.  One  hundred  pounds  of 
sulfur  mixed  with  fifty  pounds  of  air-slaked  Hme  applied  in 
the  drills  is  also  effective. 

These  methods  used  separately  or  combined  are  suffi- 
ciently established  to  warrant  general  use  on  smutted  soils 
devoted  to  onion  culture. 

Downy-mildew,  ^'"^'  ^^^  blight  {Pei^onospora  schleideni  Ung.). 
—  Close  kin  to  the  disastrous  blight  of  potatoes,  this  disease 
partakes  of  many  of  its  characters,  particularly  in  the  rapidity 
of  its  spread  through  an  infested  field.  It  may  first  be  noted 
on  a  small  area  of  the  field  in  which  the  tips  appear  as  though 
dashed  with  scalding  water.  Often  under  favorable  climatic 
conditions  the  affected  areas  increase  many  fold  in  a  single 
night,  carrying  complete  destruction. 

It  was  first  described  in  1841  by  Berkeley  as  "common 
and  destructive,"  and  has  long  been  known  to  onion  growers 


204 


Diseases  of  Economic  Plants 


in  this  country,  in  Europe,  and  in  Bermuda.  In  the  latter 
place  it  was  so  injurious  that  the  legislature  applied  to  the 
mother  country  for  investigation   and 

)i  aid.     The   first   reference   to  it  in  the 

I         ,       United  States  was  in  1872,    It  is  now 
1         /        reported  from  coast  to  coast. 
B      /  The   blight   was    described   fully   by 

Thaxter  in  1889,  again  by  Whetzel  in 
1904,  during  which  latter  year  it  was 
particularly  destructive  in  New  York, 
causing  a  loss  of  half  the  yield,  even 
more  in  some  instances. 

The  attack  in  the  field  occurs  first 
upon  a  few  plants  during  warm,  damp 
weather.  Examined  while  the  dew  is 
still  present,  these  plants,  seen  from 
considerable  distance,  display  a  peculiar 
violet  tint  especially  easy  to  discern 
through  the  dewy  covering.  Close  ex- 
amination shows  the  affected  part  to 
be  covered  with  a  fuzzy  coating.  On 
the  second  day  these  parts  lose  their 
green  color,  turn  pale,  or  even  yellow. 
On  the  third  or  fourth  day  the  plant  is 
entirely  collapsed. 

The  diseased  spots  in  the  field  may 
each  cover  an  area  of  only  a  few  feet  in 
diameter,  enlarging  slowly.  If  the 
weather  favors  the  fungus,  the  disease 
may  sweep  rajiidly  across  the  whole 
field.  Affected  plants,  under  suitable 
weather  conditions,  brilliant,  dry  atmo- 
sphere, recover  slowly,  putting  out 
new  leaves.  Subsequent  attacks  may  occur  if  the  weather 
favors  the  growth  of  the  fungus.  The  injury  from 
this  disease  is  through  the  loss  of  leaf  surface,  thus  re- 
ducing the  growing  power  of  the  plant.    Usually  little  or 


Fig.  108.  —  Onion 
plant  illustrating 
manner  of  death 
of  leaves  affected 
with  downy-mil- 
dew. After  Whet- 
zel. 


Vegetable  and  Field  Crops  205 

no  increase  in  the  size  of  the  bulb  occurs  after  a  severe 
attack. 

To  prevent  the  spread  of  the  disease,  and  to  lessen  the 
danger  from  subsequent  attacks,  a  spray  of  Bordeaux  mix- 
ture, 5-5-50,  should  be  applied  as  soon  as  the  disease  is 
noticed.  Careful  supervision  and  spraying  to  check  re- 
newed attacks  of  the  fungus,  particularly  if  the  weather 
continues  to  favor  its  development,  should  not  be  neglected. 
New  growth  should  also  be  protected  by  the  use  of  Bor- 
deaux mixture. 

Infection  in  previous  years  warrants  spraying  before 
the  disease  appears;  also  throughout  the  season,  reaching  all 
sides  of  the  leaf  with  the  fine  spray  and  using  high  pressure 
to  make  the  mixture  adhere  to  the  smooth  onion  leaves. 
Wet  lands  are  more  subject  to  this  disease  and  should  be 
avoided  if  possible.  It  is  recommended  to  rake  and  burn 
the  dead  tops,  to  destroy  the  infective  spores  within  them, 
and  to  practice  crop  rotation. 

Black-spot  ^^^  (Cleistothecopsis  circinans,  S.  &  T.,  Volu- 
tella,  also  known  as  Vermicularia  and  Colletotrichum) .  — 
The  outer  scales  of  the  bulb  after  harvest  often  show 
black  growths  of  peculiar  and  striking  character.  They  con- 
sist of  central,  black  dots  or  very  small  rings,  around  which 
from  one  to  several  larger  rings  are  arranged  concentrically. 
Under  moist  conditions  these  markings  enlarge  rapidly  by 
the  production  of  more  rings  or  wavy  lines,  or,  under  some 
circumstances,  the  whole  area  may  be  overgrown  with  black. 
Later  the  disease  may  extend  through  the  outer  bulb  scale 
and  into  the  next  and  succeeding  layers  to  considerable 
depth,  causing  rot. 

While  the  disease  is  not  conspicuous  before  harvest,  it  is 
really  present  in  the  incipient  stage  upon  the  bulbs  in  the 
field  and  continues  to  develop  rapidly  under  storage  con- 
ditions. Here  it  may  pass  to  new  bulbs  by  contact  or  by 
air  currents.  These  dangers  are  much  augmented  by  a 
moist  atmosphere.  While  the  growth  is  not  retarded  ap- 
preciably by  this  disease,  the  value  of  the  onion  is  often 


206 


Diseases  of  Economic  Plants 


much  reduced  by  the  disfiguring  spot,  and  the  loss  from  rot 
induced  by  it  is  also  considerable. 

Onions  before  they  are  placed  in  storage  should  be  well 
dried.  Storage  bins  with  good  ventilation,  so  arranged 
as  to  prevent  all  heating  or  sweating  of  the  bulbs,  should 
be  provided.  No  infected  bulbs  should  be  stored,  since 
they  will  carry  infection  to  the  sound  bulbs.     Bins  that 


Fig.  109.  —  Black-spot  on  onion.    Original. 


are  known  to  be  infested,  i.  e.,  which  held  infected  onions 
in  any  preceding  year,  should  be  disinfected  by  a  thoi'ough 
spraying  with  Bordeaux  mixture  or  plain  bluestone  solu- 
tion. The  white  varieties  of  onions  are  much  less  resistant 
than  the  rod  and  yellow  kinds. 

Neck-rot  -''^  (Botrytis  alUi  Munn).  —  This  rot  is  generally 
distributed  in  onion  sections  of  the  United  States  and  Europe, 
and  causes  heavy  losses  to  stored  onions  as  well  as  to  crops  in 


Vegetable  and  Field  Crops 


207 


the  field.    The  neck  of  the  onion,  where  the  top  has  been  cut 
off,  is  coated  with  a  fuzzy,  pale  brown  or  gray  mold,  and  later 


Fig.  110.  —  Black-spot  showing  variation.     Original. 

this  area  bears  few  or  many  black  sclerotia.    The  mold  oc- 
curs also  in  water-soaked  spots  on  leaves  and  seed  heads. 

Diseased  bulbs  should  never  be  set  out.  All  diseased  refuse 
should  be  destroyed.  The  crop  must  be  thoroughly  cured 
and  dry  before  storage. 


208 


Diseases  of  Economic  Plants 


Soft-rot -''''  (Bacillus  carotovorus) .  —  This  soft-rot,  first 
noted  in  New  York  in  1898,  is  a  common  cause  of  loss  of 
onions.    In  many  fields,  one-third  to  one-half  of  the  crop  is 


Fig.  111.  —  Botrytis  sclerotia  at  necks  of  bulbs. 
After  Munn. 


destroyed,  and  the  balance  of  the  crop  injured  by  the  pres- 
ence of  the  rot. 

Frequently  a  single  leaf  scale  of  an  otherwise  sound  onion 
is  entirely  rotten,  or  again  several  scales  may  be  rotted.  If 
the  outer  scale  is  rotted,  the  bulbs  are  designated  by  the 
growers  as  "slippery  onions."    The  rot  does  not  spread  from 


Vegetable  and  Field  Crops 


209 


Fig.  112. — Onions  affected  with  soft-rot;  longitudinal  and  cross  sec- 
tion.   After  Stewart. 


-4 

^ 

! 

i     'r 

"^ 

W^ 

Fig.  113.  —  Black-mold  due  to  Sterigmatocystis.    Original. 


210  Diseases  of  Economic  Plants 

scale  to  scale  within  the  bulb.  In  dry  onions  in  storage  its 
progress  is  slow,  but  wet  onions  decay  rapidly.  The  only 
suggestion  toward  control  is  to  keep  onions  dry  in  storage. 

Minor  diseases 

Black-mold  (Macrosporium  parasiticum  Thiim.  and  M. 
porri  Ell.).  —  Frequently  onion  leaves  that  have  been  in- 
jured assume  a  velvety,  black  coating,  which  often  appears  in 
spots,  or  covers  them  entirely.  Treatment  against  other 
diseases,  and  maintenance  of  the  plants  in  full  vigor  is  of 
most  service  in  this  case.  Another  cause  of  black-mold  -^^  is 
Sterigitiatocystis  nigra  v.  Tiegh.  It  most  commonly  appears 
forming  dark  masses  of  spores,  resembling  a  smut,  under  the 
outer  scales  of  the  bulb.  In  this  form,  the  injury  is  due  only 
to  unsightliness.  Frequently,  however,  the  fungus  grows 
into  the  lower  scales  of  the  onion,  causing  a  slimy,  soft  rot. 
It  is  not  essentially  a  field  disease,  but  one  of  chief  importance 
during  storage.  Sanitary  measures  to  prevent  the  develop- 
ment of  the  mold  on  refuse  in  the  field  are  advised.  Infested 
sacks,  crates,  bins,  etc.,  should  be  disinfected.  Pink-root  -^^ 
(Fusarium  malli  Taub.).  —  The  affected  roots  turn  yel- 
low, later  pink,  then  dry  up.  New  roots  that  develop 
also  become  diseased.  The  bulbs  are  dwarfed.  The  loss 
sometimes  is  as  great  as  40  per  cent  of  the  crop.  The 
infection  comes  from  the  soil,  and  the  general  remarks 
under  soil  diseases  (p.  26)  apply  here.  Two  rusts  occur, 
Pucdnia  porri  (Sow.)  Wint.  on  the  chive,  P.  allii  DC.  on 
onions. 

PARSLEY.    See  celery. 
PARSNIP.    See  celery. 

PEA 

Spot  '^^  {Mycosphcerella  pinodes  Berk  &  Blox.,  Asco- 
chyta).  — Spotting  of  pea  leaves  and  pods  has  been  known  to 


Vegetable  and  Field  Crops 


211 


farmers  for  many  years.  It  is  most  conspicuous  upon  the  pods 
as  circular,  somewhat  sunken  spots,  3-6  mm.  in  diameter, 
which  are  dark  bordered,  pale  in  the  centers,  or,  when  ma- 


FiG.  114.  —  Pea  leaves  showing  the  spot  disease.    After  van  Hook. 


ture,  somewhat  pink.  In  these  spots  numerous  pycnidia  are 
visible  and  under  favorable  conditions  the  spore  masses 
issuing  from  them  may  be  seen  with  the  naked  eye.    Upon 


212 


Diseases  of  Economic  Plants 


the  leaves,  similar  oval  spots,  3-10  mm.  in  diameter,  with 
the  pycnidia  usually  in  concentric  circles,  are  abundant. 
The  lower,  older  leaves  are  affected  first,  resulting  in  their 
death.  The  younger  leaves  die 
later.  Stems  are  subject  to  the 
same  attack  —  first  near  the 
ground,  later  upon  all  parts;  the 
spots  often  penetrating  through 
the  woody  part,  thus  causing 
wilting  and  death  of  the  parts 
beyond.  The  stem  attack  is  the 
most  serious  form,  since  it  di- 
rectly causes  death  to  a  large 
part  of  the  plant.  This  is  espe- 
cially true  if  the  disease  be  fol- 
lowed by  dry  weather. 

All  forms  of  the  disease  tend  to 
decrease  the  yield  in  proportion 
to  their  prevalence.  Plants  not 
Ivilled  before  flowering  may  de- 
velop pods,  though  of  lessened 
yield. 

Disease  upon  the  pod  may 
penetrate  completely  through  it 
and  appear  upon  the  opposite 
side,  or  more  frequently  it  may 
grow  into  the  seed  within  the 
pod.  Seeds  badly  diseased  in 
this  manner  adhere  to  the  pod; 
if  less  affected,  they  thresh  out, 
according  to  the  color  of  the 
variety,  more  or  less  discolored  spots.  Often  seeds  are 
diseased,  and  yet  so  slightly  disfigured  as  to  escape  ob- 
servation. 

Trial  has  demonstrated  that  of  badly  infested  seeds  only 
6  per  cent  are  capable  of  germination,  and  that  even  when 
they  do  germinate,  the  resulting  plants  seldom  reach  ma- 


FiG.  115.  —  Spotted  pods  of 
French  June  field  pea. 
After  van  Hook. 

are    shrunken,   and    show. 


Vegetable  and  Field  Crops  213 

turity.  On  young  plants  the  disease  often  assumes  the 
character  of  damping-off. 

Aside  from  the  pea  this  disease  attacks  alfalfa,  bean,  and 
hairy  vetch.  It  was  a  grave  menace  in  Europe  in  1894,  in 
Canada  in  1903,  in  Ohio  in  1904.  In  New  York,  in  1906,  from 
50  to  80  per  cent  of  the  crop  was  injured. 

Two  years'  rotation  in  nonsusceptible  crops  lessens  the 
evil.    Diseased  seed  should  be  avoided. 

Bacterial-blight  -'^'  (Pseud ornonas  pisi  Sack.).  —  The  stems 
are  discolored,  watery,  olive-green  to  olive-brown;  the  leaflets 
and  stipules  appear  bruised  and  yellow.  The  disease  is 
known  in  Colorado,  Nebraska,  Dakota,  and  Utah,  and  in 
severe  outbreaks  has  been  known  to  kill  30  per  cent  of 
the  plants. 

Wilt  (Fusarium  sps.).  —  Two  wilts,  both  due  to  Fusarium, 
have  been  described.  They  agree  essentially  with  the  de- 
scription under  cowpea. 

Minor  diseases 

Powdery -mildew  (Erysiphe  polygoni  DC.)  develops  most 
conspicuously  late  in  the  season,  and  sometimes  becomes  so 
injurious  that  the  plants  do  not  mature  seed.  Though  it  is 
not  usually  very  destructive,  20  per  cent  injury  has  been 
reported  from  Ohio;  33  per  cent  from  some  parts  of  Nebraska. 
The  fungus  hibernates  in  seed  derived  from  affected  pods. 
Such  seed  should  not  be  used  for  planting.  Liver  of  sulfur  or 
Bordeaux  mixture  is  effective  in  the  field. 

Black-mold  (Pleospora  pisi  (Sow.)  Fcl.).  —  Frequently 
moldy,  black  spots  are  noted  upon  pea  pods,  leaves,  or  other 
parts.  This  condition  is  chiefly  a  secondary  disease  following 
some  other  injury. 

Stem-rot  (Corticium  vagum)  is  somewhat  injurious,  as  is 
also  the  Root-rot  {Thielavia),  and  Root-knot  (nematodes). 

Damping-ofif.    See  p.  19. 

Rust  is  rare  on  pea.    See  bean. 


214  Diseases  of  Economic  Plants 

PEANUT 

Leaf-spot  (Cercospora  personata  (B.  &  C.)  Ell.).  —  This 
leaf-spot  is  circular  in  outline,  indefinitely  bordered,  black 
to  brown  in  the  center  and  grading  to  green  on  its  outer 
edge.  The  lower  leaves  are  first  affected  and  suffer  most; 
later  the  disease  spreads  to  the  upper  leaves.     The  leaves 


s        2!»     -  -        <* 


:0'^'   :jk  ■* 


>^ 


Fig.  116.  —  Peanut  leaf-spot.    After  Wolf. 

begin  to  fall  soon  after  they  spot,  and  in  many  cases  the 
death  of  the  plant  results.  It  is  often  a  pest.  The  causal 
fungus  was  first  collected  in  Carolina  and  Alabama  by 
Ravenel. 

Southern-blight  {Sclerotium  rolfdi)  does  some  damage. 
(See  pp.  23,  215.)  The  true  rust  (Uredo  arachidis  Lag.)  is 
injurious  in  the  sub-tropics.  Red-rot  of  the  pods,  charac- 
terized by  brown  discoloration  and  tlie  presence  of  red 
perithecia  (Neocostnospora)  is  of  slight  importance. 


Vegetable  and  Field  Crops 


215 


PEPPER 


Southern-blight,  wilt  ^^  {Sclerotium  rolfdi  Sacc).  —  Blight 
shows  itself  first  by  a  slight  drooping  of  the  leaf  tips  by  day, 


1' 

mw 

X 

hItkI 

wk 

■^L/Xnt 

ml   ' 

*  V- 

%:■ 

liG.  117.  — -Pepper  plant  showing  effects  of  the 
Southern-bhght.    After  Fulton. 


followed  by  night  recovery.  The  wilt  becomes  more  pro- 
nounced on  succeeding  days  until  in  the  third  or  fourth  day 
the  leaves  wilt  permanently,  lose  color,  dry,  and  soon  fall. 
These  stages  may  succeed  each  other  so  rapidly  as  to  ap- 
pear almost  simultaneous.  The  roots  appear  normal;  but 
on  the  stem   near   the   ground    are   found   shrunken,   dis- 


216 


Diseases  of  Economic  Plants 


colored  areas  in  the  bark,  often  extending  part  of  the  way 
around  the  stem.  Later  the  roots  may  rot  from  secondary 
causes. 

Upon  the  diseased  spots  are  fine  mycelial  strands,  espe- 
cially abundant  under  humid  conditions.    Soon  these  strands 

unite  into  tufts,  which 
round  off,  become  hard 
and  smooth,  and 
change  from  white  to 
yellow,  and  finally  to 
dark  brown.  These 
bodies,  the  sclerotia, 
are  about  as  large  as 
mustard  seeds.  At- 
tacks usually  begin 
when  the  pods  are 
forming  and  continue 
throughout  the  season. 
This  disease  has  been 
found  in  many  South- 
ern states  upon  a  wide 
range  of  plants.  See 
p.  23. 

The  application  of  a 
clear,  preventive  fun- 
gicide, such  as  ammo- 
niacal  copper  carbon- 
ate, to  the  ground  at 
the  base  of  the  plant,  and  where  any  part  touches  the 
ground,  so  that  it  can  soak  into  the  ground  near  by  and 
cover  the  stem  itself,  has  proved  beneficial.  The  first  ap- 
plication should  be  made  at  the  earliest  sign  of  blight,  or 
still  better,  in  anticipation  of  it,  and  should  be  followed  by 
other  apphcations  at  intervals  of  two  to  three  weeks.  Bor- 
deaux mixture  is  not  suitable,  since  the  effective  material  is 
filtered  out  by  the  soil. 

Black-mold  (Macrosporiuni  sp.).  —  This  malady  renders 


.^^ 

u. 

f 

w 

W'J 

w 

/      ""^ 

Fig.  118.  —  Pepper    plant  showing   fun- 
gus of  Southern-blight.     After  Fulton. 


Vegetable  and  Field  Crops  217 

the  fruit  moldy  and  black,  particularly  at  the  blossom  end. 
It  is  one  of  the  most  destructive  of  pepper  diseases. 

Minor  diseases 

Anthracnose  (Glomerella  piperata  (E.  &  E.)  S.  &  S.,  Gloeo- 
sporium).  —  Soft,  circular,  pale,  sunken  spots  upon  the  fruit 
accompanied  by  small,  ruptured  spots  in  the  skin,  through 
which  the  pink  spore  masses  protrude,  indicate  this  disease. 
Anthracnose  due  to  Colletotrichum  nigrum  E.  &  H.  is  of 
similar  appearance  except  that  the  centers  of  the  soft  spots 
change  to  a  decided  black  as  they  age.  Mosaic  similar  to 
that  of  tobacco  is  often  present.  Black-spot,  caused  by 
Alternaria  entering  through  wounds  due  to  sun-scald  or 
frost,  sometimes  injures  45  per  cent  of  the  fruits.  A  Fruit- 
rot  is  caused  by  Sderotium  hataticola  Taub.  Leaf- spot 
(Phyllosticta  sp.)  shows  small,  circular  spots  of  ashen  color, 
bearing  pycnidia.  Other  diseases  are:  Leaf-spot  (Cercos- 
pora  capsici  H.  &  W.),  Soft-rot  (bacteria),  Root-knot 
(nematodes) . 

POTATO 

-  Late-blight  -*'«--^^'  ^'^-  (Phijtophthora  infestans  (Mont.)  De 
Bary).  —  In  the  year  1889  Lamson-Scribner,  writing  of 
this,  the  most  serious  potato  disease,  said,  "  It  prevails  in  all 
potato  countries  of  the  world,  and  causes  more  damage  to  the 
potato  than  all  other  injuries  coml^ined."  It  is  possible  that 
all  that  he  regarded  as  blight  would  not  to-day  be  included 
under  late-blight;  still  the  disease  holds  its  place  as  one  of 
the  most  destructive  plant  diseases  of  the  world. 

It  is  estimated  that  in  New  York  state  alone  the  blight 
caused  a  loss  of  $10,000,000  in  1912,  and  the  total  loss  in  the 
United  States  in  1917  is  placed  at  24,000,000  bushels.  The 
loss  reported  in  one  year  from  Ohio  was  $2,000,000;  from 
Wisconsin  $5,000,000.  The  l)light  is  supposed  to  have 
originated  in  South  America  antl  to  have  been  brought  to 
this  country  about  1840. 

The  disease  may  appear  on  any  part  of  the  leaf,  but  the 


218 


Diseases  of  Economic  Plants 


spots  generally  show  first  near  the  tip  or  margin,  probably 
because  surface  water  remains  longer  on  these  parts.  The 
diseased  area  soon  blackens  and  dies.  The  diseased  part  may 
temporarily  dry  out  and  curl  up  if  the  progress  of  the  fungus 
is  checked  by  drought,  or  the  blight  may,  in  rainy  weather, 
rapidly  proceed  to  transform  the  entire  foliage  into  a  moist, 


Fig.  119.  —  Potato  late-blight.  Eows  at  left  sprayed  with  Bordeaux 
mixture  and  Paris  green;  rows  at  right  received  Paris  green  only. 
Original. 

putrid  mass.  In  the  earlier  stage  the  blackened  part  is 
bordered  by  a  narrow  region  of  light  green,  characterized 
by  a  slightly  watery,  flaccid  appearance.  Under  conditions 
of  especially  humid  atmosphere  a  fine,  white  down  may  be 
seen  upon  the  more  recently  invaded  parts.  This  affection 
of  the  leaves  is  accompanied  by  an  offensfve  odor  discernible 
at  consideral)le  distance  from  the  field.  The  disease  usually 
soon  shows  on  the  stems  also,  which  in  turn  blacken  and  die. 


Vegetable  and  Field  Crops  219 

On  the  surface  of  tlie  tul)er  slightly  depressed,  dark- 
colored  areas  appear  wliile  internally  the  normal  white  color 
changes  to  dirty  brown.  If  the  soil  is  dry,  dry  rot  results; 
if  wet,  the  tubers  decay  as  wet,  slimy,  ill-smelling  masses. 
In  storage  the  disease  continues,  and  the  loss  sustained  in 
the  field  may  be  greatly  augmented. 

This  blight  is  closely  dependent  upon  conditions  of  heat 
and  moisture.  A  daily  mean  of  22°  to  23°  C.  (72°-74°  F.) 
accompanied  by  moist  weather  conduces  to  its  spread.  A 
daily  mean  temperature  above  25°  C.  (77°  F.)  for  a  few  days 
retards  its  development. 

Although  the  conspicuous  signs  above  noted  first  attract 
the  attention  of  the  general  observer,  the  disease  really 
commences  as  soon  as  the  sprouts  appear.  Young  plants 
grown  fi-om  infected  seed  remain  dwarfed,  assume  a  reddish 
brown  color,  and  when  proper  weather  conditions  obtain, 
furnish  the  spores  to  start  the  general  attack. 

Marked  difference  in  resistance  exists  among  varieties. 
Thus  in  Maine  the  Rust-proof  showed  the  highest  resistance, 
about  1  per  cent  of  disease,  while  no  other  varieties  tried  gave 
less  than  30  per  cent  of  disease.  Of  the  standard  crop  vari- 
eties the  following  are  reputed  to  possess  some  degree  of 
resistance:  Carmen  No.  3,  Sir  Walter  Raleigh,  Rural  New 
Yorker  No.  2,  Rural  Blush,  Green  Mountain,  State  of  Maine, 
Delaware,  Enormous,  and  White  Beauty. 

Field  trials  have  shown  that  certain  German  and  English 
varieties  are  more  highly  resistant  than  the  American  vari- 
eties. It  is  a  hopeful  sign,  therefore,  that  American  potato 
breeders  ai-e  now  giving  attention  to  disease  resistance  and 
that  new  varieties  of  greater  excellence  in  this  respect  may 
be  expected  in  the  future. 

Healthy  potatoes  only  should  be  used  for  seed.  Diseased 
potatoes  may  be  recognized  by  their  reddish  brown  surface 
color,  which  extends  toward  the  center  of  the  potato;  also 
by  the  slight  shrinking  of  the  suiface  in  such  parts,  or  by  the 
spotting  described  above. 

The  crop  should  be  sprayetl  as  recommended  under  the 


220 


Diseases  of  Economic  Plants 


general  heading,  p.  236.  Though  the  disease  may  not  develop 
annually  in  severe  form,  spraying  is  necessary  each  year  as  a 
preventive  measure.  Since  the  bhght  develops  rapidly,  it  is 
quite  impracticable  to  wait  for  signs  of  the  disease  before 
spraying  is  begun.  Moreover,  experiments  extending  over 
several  years  have  shown  that  even  in  years  when  the  blight 
does  not  become  epidemic,  sufficient 
l)enefit  is  derived  from  spraying  to 
warrant  its  adoption. 

The  Geneva  Experiment  Station 
says:  ''Judging  from  the  experiments 
thus  far  made,  it  appears  that  spray- 
ing for  l)light  is  an  operation  which  no 
potato  grower  in  New  York  can  afford 
to  neglect.  Forty-eight  farmers'  busi- 
ness experiments  show  an  average 
net  profit  of  $20.51  per  acre  due  to 
spraying." 

Commence  spraying  with  Bordeaux 
mixture  when  plants  are  6  to  8  inches 
high  and  repeat  at  intervals  of  ten  to 
fourteen  days  throughout  the  season, 
making,  in  all,  five  or  six  applications. 
When  Ijugs  or  flea  beetles  are  numerous,  add  Paris  green  or 
other  poison.  In  case  the  tops  have  blighted,  the  danger  of 
tuber  infection  and  consequent  rot  is  lessened  by  delaying 
the  harvest  of  the  tubers  until  at  least  a  week  or  ten  days 
after  the  death  of  the  foliage. 

Common-scab  -''2-274  (Actinomycc-!  i^cabies  (Thaxt.)  Giiss.)  — 
Scab  prevails  in  Europe,  Africa,  New  Zealand,  in  all  parts  of 
the  United  States,  and  probably  wherever  the  potato  is 
grown.  It  was  first  attributed  to  its  proper  cause  by  Thaxter 
in  1890. 

Common-scali  is  recognized  by  all  potato  growers  as  a  char- 
acteristic, rough  pitting  of  the  tubers.  If  potatoes  are  at- 
tacked when  quite  young,  the  scabs  are  deep;  if  the  attack  is 
later,  they  are  more  shallow.     In  scn^ere  cases  the  tuber  is 


Fig.  120.  —  Common 
scab  produced  by 
inoculation  forming 
monogram  R.  T. 
After  Thaxter. 


Vegetable  and  Field  Crops 


221 


furrovvetl  or  cracked.  Mites  often  follow  scab,  making  the 
pits  much  deeper. 

The  scab  at  first  appears  as  a  minute  reddish  or  brownish 
surface  spot,  often  when  the  potato  is  very  young.  It  ex- 
tends outward,  deepens  in  color,  and  is  attended  with  the 
development  of  an  irregular,  corky  incrustation. 

The  disease  is  often  prevalent  to  such  an  extent  as  to  pro- 
hibit successful  potato  culture.  The  chief  loss  comes  from  de- 
preciation in  sale  value,  though  there  is  also  loss  in  yield. 


Fig.  121. — ^  Potato  common-scab.    After  Melhus. 


Estimates  show  that  from  5  to  75  per  cent  of  the  potato  crop 
is  unsalable  on  account  of  scab.  The  loss  in  California  in  one 
county  alone  is  placed  at  $300,000  yearly. 

Common-scab  is  most  prevalent  in  alkaline  soils  and  is 
favored  by  moisture.  Wood  ashes,  potash,  soda,  stable 
manure,  lime,  etc.,  increasing  alkalinity,  favor  the  growth 
of  the  fungus,  and  cause  increase  in  the  amount  of  scab  in 
soil  already  infested.  Materials  which  tend  to  decrease  scab 
are  commercial  fertilizers,  potash  salts  (except  carbonate), 
land  plaster,  and  ammonium  sulfate.    Rotation  of  crops  tends 


222  Diseases  of  Economic  Plants 

to  diminish  the  amount  of  seal),  provided  other  susceptible 
crops,  as  beets,  turnips,  cabbages,  etc.,  are  avoided.  A 
three-year  rotation  without  a  susceptible  crop  largely  re- 
duces it,  though  after  five  or  even  ten  years  the  fungus 
may  not  be  entirely  exterminated.  During  rotation  any 
practice  that  increases  the  acidity  of  the  soil  aids  in  reduc- 
ing scab.  Thus  plowing  under  green  crops  is  a  favorable 
practice. 

In  general  it  may  be  said  that  scabby  seed  potatoes  in  any 
soil  will  produce  a  scabby  crop,  l)ut  the  amount  of  scab  is 
determined  somewhat  by  the  conditions.  Seed  potatoes  free 
from  scab,  in  a  soil  free  from  scab,  will  raise  a  crop  free  from 
scab.  Seed  potatoes  free  from  scab  will  not  produce  a  healthy 
crop  if  grown  in  infested  soil;  but  less  scab  will  result  than 
when  diseased  seed  is  used. 

There  is  much  difference  in  varietal  resistance  to  scab. 
The  more  resistant  varieties  should  be  used  on  infested 
soil. 

Two  conditions  arise  reciuiring  different  cultural  meth- 
ods:— 

1.  The  management  of  clean  soils. 

2.  The  management  of  soils  already  infested. 

If  the  land  is  free  from  infestation,  great  care  should  be 
exercised  to  avoid  introduction  of  the  scab  fungus  by  any  of 
the  general  means  suggested  under  soil  disease,  p.  26.  In 
particular,  infestation  may  occur  by  the  use  of  scabljy  seed,  or 
through  the  use  of  manure  which  has  been  infested  by  feed- 
ing uncooked,  scabby  potatoes  to  stock.  If  seed  must  be 
planted  that  cannot  safely  be  regarded  as  free  from  scab, 
and  no  seed  from  an  unknown  source  can  be  so  regarded,  it 
should  be  disinfected  to  free  it  of  scab  germs.    See  p.  240. 

No  system  of  soil  treatment  has  proved  reliable  in  the 
management  of  infested  land.  Long  rotation,  avoiding 
susceptible  root  crops,  should  be  practiced.  The  use  of 
fertiHzing  mateiials  which  favor  the  fungus  should  be  avoided 
and  resistant  varieties  should  be  planted.  The  turning 
under  of  a  green  crop,  e.  g.,  rye,  may  gradually  decrease  the 


IiG.  122.  —  Potato  badly  infested  with  wart.    After  Kunkel. 


224 


Diseases  of  Economic  Plants 


scab  tendency.    The  benefit  of  treating  seed  to  be  used  on 
infested  soil  varies  largely  with  local  conditions. 

Wart'-''^'  ^*'^'  ^^^  {Synchytrium  eridohiotiaim  (Schil.)  Perc,  also 
known  as  Chrysophlyctis) .  —  This  disease  invaded  America 
(Newfoundland)  about  1909,  and  recently  was  (Sept.,  1918) 
found  in  several  counties  of  Pennsylvania;  still  more  recently 
in  Virginia  and  West  Virginia.     It  has  long  been  known  in 


Fig.  123.  —  Potato  infested  with  powdery- 
scab.     After  Melhus. 


England  and  Europe.  Badly  diseased  potatoes  are  entirely 
replaced  by  a  white,  warty  mass;  in  milder  cases,  only  a  few 
eyes  are  affected  with  either  brown  or  black  spots,  or  with 
dark  warts  of  size  varying  from  that  of  a  pinhead,  upward. 
Soil  once  infested  must  not  be  used  for  potatoes,  neither 
may  diseased  seed  be  used.  Great  care  should  be  exercised 
to  prevent  wider  distribution  of  this  dangerous  disease  in 
America. 

Powdery-scab  -"*'  (Spongospora  subferranea  (Wallr.)  Johns.). 
—  Known  in  Europe  since  1841,  this  disease  was  first  re- 
ported in  the  United  States  in  1918,  prol)ably  having  been 


Vegetable  and  Field  Crops  225 

introduced  through  foreign  shipment  in  1911.  It  is  now 
prevalent  in  certain  parts  of  Canada  and  in  Maine,  Massachu- 
setts, Nebraska,  New  York,  Washington,  Oregon,  and 
Minnesota.  The  tubers  are  infected  when  very  young.  At 
maturity  the  infected  area  becomes  a  pit,  filled  with  dusty, 
yellow  spore-balls;  the  pit  bordered  l)y  remnants  of  the 
tuber's  skin.  The  sale  value  of  the  potato  is  decreased,  the 
yield  lessened,  and  its  value  for  seed  purposes  lost. 

Precautions  should  be  taken  to  guard  against  infected 
seed. 

Black-scurf  '-"•'•  ■-''^'  "'^  {Corticium  vagum  B.  &  C,  Rhizoc- 
tonia).  —  Though  particularly  prevalent  in  the  Middle  West 
and  Rocky  Mountain  states,  this  pest  is  also  known  generally 
in  the  East,  from  Connecticut  southward.  Infected  tubers 
are  largely  responsible  for  the  contamination  of  new  soil. 
They  may  be  recognized  by  the  superficial,  irregularly 
shaped,  scurfy,  dark-brown  patches  (sclerotia)  of  fungous 
threads  varying  in  size  from  a  pinhead  to  a  grain  of  wheat. 
They  are  seen  clearly  only  when  the  tuber  is  wet. 

Soon  after  planting  the  young  sprouts  are  attacked  by 
this  waiting  fungus.  Black  spots  appear  near  the  surface  of 
the  ground,  destroying  the  bark  and  often  girdling  the  stem. 
In  such  cases  aerial  tubers  often  form,  and  the  plants  are 
malformed  and  stunted.  A  dark  network  of  fungous  threads 
is  sometimes  seen  upon  the  subterranean  parts.  The  fungus 
advances  above  ground  and  develops  a  gray  spore-bearing 
layer  about  the  green  stem,  often  extending  upward  several 
centimeters,  causing  the  young  shoots  to  wilt,  droop,  and  die. 
Often  a  loss  of  one-fourth  to  one-third  of  the  plants  follows. 
Stems  that  survive  this  early  attack,  but  succumb  to  later 
attack,  produce  only  a  few  underground  tubers,  small  and 
unsalable. 

Stem  lesions  similar  to  those  of  black-scurf  are  also  pro- 
duced by  a  number  of  different  fungi. 

Only  clean  seed  should  be  used.  If  there  is  any  doubt,  it 
should  be  treated  as  is  recomnu^nded  for  potato  common- 
scab,  but  even  this  treatment  is  not  effective  if  large  sclerotia 


226 


Diseases  of  Economic  Plants 


are  present  on  the  seed.     Liming  the  soil,   clean   culture 
methods,  and  crop  rotation  are  palliative.     Infested  refuse 

should  be  destroyed 
by  fire.  Soil  badly 
infested  should  not 
be  planted  to  pota- 
toes. In  general,  the 
remarks  made  under 
soil  diseases  apply 
here. 

While  this  disease 
has  long  been  recog- 
nized in  Europe, 
especially  in  Ger- 
many, no  record  of  it 
was  made  in  America 
until  1891.  Since 
that  date  it  has  been 
noted  upon  many 
hosts  in  many  states. 
Sec  p.  21. 

Early-blight  27"  (AZ- 
teryiaria  solani  (E.  & 
M.)  J.&G.).— This 
is  one  of  the  very 
serious  potato  dis- 
eases. In  1906  the 
loss  in  Wisconsin  was 
placed  at  about 
5,000,000  bushels, 
and  a  50  per  cent  loss 
was  reported  from 
Wyoming.  The  average  loss  in  Michigan  is  estimated  as  25 
per  cent  of  the  crop.  It  is  known  throughout  the  United 
States,  in  Europe,  Africa,  and  Asia. 

The  grayish-l)r()vvn  leaf-spots,  which  are  brittle,  irregularly 
circular,  and  concentrically  marked,  appear  about  the  time 


Fig.  124. 


Little  potatoes  and  aerial  pota- 
toes.   After  Rolfs. 


Vegetable  and  Field  Crops 


227 


the  tubers  begin  to  form.  The  coalescence  of  the  spots 
involves  large  areas  of  leaf  tissue  and  results  in  browned, 
withered  leaves,  the  stems  remaining  green.     The  illusion 


125.  — ■  Potato  attacked  by  Corticium. 
After  Rolfs. 

is  often  so  complete  as  to  lead  the  grower  to  think  that  the 
vines  have  died  a  natural  death.  The  progress  of  the  disease 
is  slow,  three  or  four  weeks  intervening  before  all  the  leaves 
are  dead.  The  loss  of  efficient  leaf  tissue  so  diminishes  the 
vigor  of  the  plant  that  the  yield  is  largely  reduced.    Early- 


228 


Diseases  of  Economic  Plants 


blight  is  also  serious  on  tomatoes  in  the  South,  on  leaves  and 
on  fruits,  where  it  produces  a  rot.  It  is  found  also  upon 
eggplants.  This  is  a  disease  characteristic  of  dry  soils  and 
seasons,  and  is  likely  to  be  associated  and  confounded  with 
tip-burn. 

General  spraying  (p.  236)  will  hold  this  blight  in  check. 
Tip-burn. -^^'  ^-^  —  Leaves  die  at  the  edges  and  tips,  curl 
somewhat,   and   eventually   the   whole  top   withers.     This 
condition  occurs  when  the  sun 
is  hot  and  the  winds  dry,  and 
is  especially  noticeable  when 
a  cool,  wet  period  is  followed 
by  hot,  dry  weather.     It  has 
been  asserted  that  the  primary 
cause  is   attack  by  leaf-hop- 
p(^rs.     Though  not  due  to  a 
parasite,   spraying  with  Bor- 
deaux mixture  lessens  the  loss. 
^ilt   2^0-  477.  531     ^Fusarium 
oa-yftponmi  Schl.  and  Fusarium 
.s/;,s'.). — This  wilt  is  definitely 
known  in  many  states,  and  is 
probably  identical  with  a  very 
destructive  potato  disease  of 
England,    Germany,    France, 
and  Belgium. 
When  the  plants  are  about  a  foot  high,  or  in  mild  cases  a 
little  later,  the  first  trace  of  the  wilt  is  noticeable.     The 
leaves,  which  are  usually  light-colored,  assume  a  dull,  un- 
healthy appearance,  with  rolling  or  curling  of  the  margins. 
Progressive  disease  gradually  causes  the  top  to  fall,  and 
gives  a  general  effect  of  premature  ripening.     When  the 
diseased  plants  are  pulled  up,  the  partially  dead  roots  are 
found  to  be  quite  brittle,  and  frequently  bear  a  white  or  pink 
mold.    If  the  imderground  portion  of  the  stem  is  cut  across,  a 
pronounced  l)rown  discoloration  is  visible.    This  brown  stain 
is  also  found  in  the  l>ranches  leading  to  the  tubers,  and  a  thin 


Fig.   126. —  Potato    early-blight 
spots  enlarged.   After  Whetzel. 


Vegetable  and  Field  Crops 


229 


slice  across  the  stem  end  of  the  tuber  will  often  reveal  its 
presence  there  as  well. 


Fig.  127.  —  Tip-burn.    After  Wis.  Agr.  Exp.  Sta. 

The  loss  amounts  to  millions  of  dollars  annually,  due: 
(1)  to  deficient  germination;  (2)  to  earlj^  ripening  and  thus 
to  diminished  yield;  (3)  to  rot  in  storage. 


230  Diseases  of  Economic  Plants 

When  the  potatoes  are  dug,  there  is  rarely  any  external 
evidence  of  the  disease.  The  major  portion  of  the  crop  pro- 
duced from  wilted  plants  is  nevertheless  infected.  If  these 
potatoes  are  stored  in  a  cold  place,  but  little  change  occurs; 
but  when  infected  potatoes  are  kept  in  a  heated  room  or 
left  out-of-doors  in  a  warm  climate,  rot  soon  develops. 

The  presence  of  this  disease  can  be  detected,  in  otherwise 
normal  tubers,  only  by  making  a  thin  slice  across  the  stem 
end  and  searching  for  the  brown  discoloration.  Such  pota- 
toes are  not  desirable  for  seed,  but  are  not  objectionable  for 
food. 

Soils  which  have  once  borne  a  sick  crop  will  infect  future 
crops.  The  general  means  by  which  a  field  may  become 
infested  are  discussed  on  page  27.  In  addition  to  these 
means,  the  potato  wilt  is  often  carried  to  new  fields  by  seed. 
It  is  a  matter  of  record  that  this  disease  was  largely  in- 
troduced into  California  from  Oregon  by  means  of  infected 
tubers.  This  could  have  been  prevented  by  proper  quaran- 
tine restrictions. 

If  potatoes  must  be  stored  for  any  length  of  time,  all  that 
are  badly  diseased  should  be  rejected,  and  the  remainder 
kept  as  cool  as  possible  without  freezing.  It  is  best  to  sell  or 
consume  all  affected  tubers  at  once. 

Another  very  similar  wilt  is  due  to  Vertidllium  alboatrurn 
Reink.  Several  types  of  tuber  rot  due  to  various  Fusaria 
are  distinguished,  e.  g.,  the  jelly-end-rot,  a  soft  rot  of  the 
stem  end;  dry-rot,  also  of  the  stem  end.  A  tuber  dry-rot  is 
also  caused  by  Phoma. 

Wilt  ^'*'  (Pseudo7nonas  solanacearuni  (EFS.)).  —  This  wilt, 
chiefly  prevalent  from  Maryland  southward,  reported  also 
from  Indiana,  Nebraska,  and  Iowa,  is  identical  with  that  of 
eggplant,  toliacco,  and  tomato,  and  is  to  a  large  extent 
transmitted  by  insects. 

The  leaves  wilt  and  dry  up;  the  stems  and  tubers  show 
yellowing  and  l)lackening  in  the  veins,  and  the  tubers  give 
way  to  a  soft  rot.  Squeezing  the  fliseased  tubers  causes  ex- 
udation of  creamy  drops  from  the  diseased  veins. 


Vegetable  and  Field  Crops 


231 


Tubers  from  diseased  vines  rot  rapidly  and  should  not 
be  stored.  If  stored,  they  should  be  kept  at  as  low  a  tempera- 
ture as  possible.  It  is  unwise  to  plant  potatoes  in  land  which 
has  shown  this  disease  upon  any  of  its  hosts,  without  a  long 
intervening  rotation.    The  precautions  suggested  under  soil 

use    of     clean 


seed,  and  special  atten- 
tion to  insect  control, 
are  preventive  measures. 
Black-leg  ''"'•"'  -^^-  -^^'  ^^^^ 
(Bacillus  phytophihorus 
Appel).  — •  Much  confu- 
sion has  arisen  concerning 
the  identity  of  black-leg, 
since  in  many  instances 
the  mere  occurrence  of 
a  black  region  upon  the 
stem  near  the  ground 
line  has  led  to  the  use  of 
the  term.  It  is  thus 
probable  that  in  the 
literature  of  potato  mal- 
adies several  distinct  dis- 
eases have  been  confused 
with  black-leg. 

A  distinct,  definite, 
and  serious  disease  has,  however,  been  known  in  Europe 
and  England  for  several  years  under  this  name.  Jones, 
who  studied  black-leg  in  the  field  in  Germany  and  England 
and  what  appeared  to  be  the  same  disease  in  Vermont, 
described  it  essentially  as  follows:  The  earliest  conspicuous 
symptom  was  that  the  diseased  plants  were  slightly  be- 
low normal  size,  of  a  paler  or  yellowish-green  color,  the 
lateral  branches  and  petioles  becoming  more  erect  and 
the  leaf  blades  curving  upward,  giving  the  entire  plant  a 
narrowed  aspect.  The  lower  leaves,  in  the  meantime,  have 
possibly  shriveled  and  died.     The  stem  was  more  or  less 


Fig.  128.  —  Dry-rot   caused  by  Fusa- 
rium.    After  Coons. 


232 


Diseases  of  Economic  Plants 


browned  or  blackened  from  near  the  surface  of  the  soil  down- 
ward. In  extreme  cases  the  discoloration  was  visible  2-3  cm. 
above  the  soil.    The  tissues  of  the  discolored  part  died,  and 


the  softer  parts  decayed.  Usually  the  seed  tuber  also  was 
rotted.  Loss  as  high  as  20  per  cent  is  reported  in  Maine, 
75  per  cent  in  certain  fields  in  Michigan ;  but  such  large  loss 
is  unusual. 

The  disease  is  carried  over  to  succ(HM:ling  crops  in  the  seed, 


Vegetable  and  Field  Crops 


233 


and  is,  therefore,  of  greatest  importance  to  growers  of  seed 
potatoes.  Seed  should  be  carefully  selected,  and  then  dis- 
infected. 

Leaf-roll  -^'  -^  '^^^^  ■'^'^'  -'-^^  (Phloem-necrosis)  and  Mosaic 
(Leaf-curl  or  Curly-dwarf) ,  two  closely  related  diseases  of  wide 
distribution,  cause  serious  crop  loss.  In  Bermuda,  for  exam- 
ple, the  loss  from  leaf-roll  is  estimated  to  be  well  above  50 


Fig,  130.  —  Potato  leaf-roll.    After  Orton. 


per  cent  of  the  crop.  The  two  diseases,  formerly  regarded  as 
three,  are  difficult  to  distinguish  accurately  without  the  use 
of  the  microscope,  but  in  general  in  leaf-roll  the  segments  of 
the  lower  leaves  are  pale,  permanently  rolled  upward  and 
rigid,  the  terminal  segments  becoming  spoon-shaped;  while  in 
mosaic,  generally,  the  leaf  segments  are  distorted,  the  veins 
unduly  prominent,  and  the  blades  mottled  with  light  areas, 
and  in  severe  cases  the  plants  tlwarfed  by  shortened  inter- 
nodes,  giving  rise  to  the  designation  "Curly-dwarf."  Plants 
affected  by  either  of  these  diseases  show  retarded  tuber 
development  and  reduced  yield. 


234  Diseases  of  Economic  Plants 

Both  diseases  are  usually  of  such  mild  form  during  the 
first  year  as  to  be  unnoticed;  but  appear  in  much  more 
severe  form  during  the  second  year.  Though  the  causal 
organism  is  unknown,  both  are  also  contagious,  and  infection 
passes  readily  from  plant  to  plant  in  the  field.  Such  infection 
takes  place  chiefly  through  the  soil  and  has  been  observed  to 
occur  at  a  distance  of  2  meters.  The  disease  is  seed-borne  and 
probably  infestation  does  not  persist  in  the  soil.  Therefore 
seed  should  be  taken  from  a  field  free  of  these  diseases,  or 
seed-plants  which  grew  fully  2  meters  distant  from  diseased 
plants  should  be  selected. 

Minor  diseases 

Leaf-blotch  -^^  (Cercospora  concors  (Casp.)  Sacc.)  appears 
when  the  plants  begin  to  blossom.  The  lower  leaves  show 
obscurely  defined,  pale  spots,  3-5  mm.  in  diameter,  these 
sometimes  blending  to  form  larger  areas.  The  spots  some- 
times much  resemble  the  early-blight  spot,  but  more  often  the 
entire  leaf  slowly  turns  yellow  and  dies.  The  damage,  espe- 
cially to  late  potatoes,  is  considerable. 

Leak  -^-  {Rhizopus  nigricans  Ehr.  and  Pythium,  deharyanum 
Hesse.).  —  Orton  has  described  a  wet,  soft  rot  of  potato  in  the 
peat  lands  of  California.  It  is  characterized  by  dull  brown 
discoloration  of  the  skin  and  light  brown  or  buff  coloring  of 
the  flesh,  accompanied  by  softening.  Upon  pressure  a  clear 
brown  liquid  without  disagreeable  odor,  exudes. 

The  disease  spreads  rapidly  in  warm  weather,  and  entire 
shipments  may  decay  en  route  to  market.  To  prevent  infec- 
tion the  skin  should  not  be  broken  in  handling,  and  all  refuse 
should  be  destroyed  by  fire.  Diseased  tubers  should  be  scru- 
pulously sorted  out  of  lots  intended  for  storage  or  shipment. 

Silver-scurf  {Spondylocladiimi  atrovirens  Harz.).  —  Dark 
blotches  spotted  with  minute  black  specks  appear  on  the 
surface  of  the  tubers.  Later  these  assume  a  silvery-gray  tint. 
The  disease,  recently  introduced  from  Europe,  is  widely 
distributed,  but  n^t  of  great  importance.  Infected  seed 
should  not  be  used. 


Vegetable  and  Field  Crops 


235 


Black-heart.-^^'  -'•'"  —  The  centers  of  the  tubers  turn  black 
or  become  hollow  with  a  black  lining.  This  is  due  to  ab- 
normal physical  conditions,  such  as  high  temperature,  or 
deficiency  of  oxygen,  and  occurs  mainly  in  potatoes  stored  in 
artificially  heated  rooms,  or  piled  too  deep  (over  6  ft.). 
Temperatures  above  35°  C.  (95°  F.)  should  be  avoided,  and 
ventilation  provided. 


Fig.  131.  —  Black-heart  of  potato  caused  by  exclusion  of  air.     After 
Stewart  and  Mix. 

Spindling-sprout,  the  cause  of  which  is  unknown,  is  a 
diseased  condition  in  which  the  normal  stout  thick  sprouts 
fail  to  develop  and  in  their  stead  are  slender  abnormally  long 
sprouts.  Seed  potatoes  affected  with  this  disease  result  in  an 
uneven  stand  with  many  missing  hills,  weak  plants,  and  cor- 
responding decrease  in  yield. 

Hollow-heart. — In  years  of  abundant  rainfall  large  pota- 


236  Diseases  of  Economic  Plants 

toes  frequently  show  cavities  at  the  centers,  lens-shaped 
clefts  with  browned  linings,  due  apparently  to  tension  result- 
ing from  unequal  growth.  Though  this  is  not  a  true  disease 
such  tubers  are  discriminated  against  in  grading.  Varieties 
subject  to  this  trouble  should  be  planted  closely  since  crowd- 
ing helps  to  overcome  the  tendency. 

Internal  brown-spot,  scattered,  rusty  brown  spots,  2-10 
cm.  in  diameter,  occur  irregularly  throughout  the  potato. 
No  parasite  is  present  and  the  diseased  condition  is  not  trans- 
mitted through  the  seed.  However  seed  showing  this  chai- 
acter  should  be  avoided. 

Net-necrosis.  —  Netted,  brown  or  black  areas,  beginning  at 
the  stem  end,  extend  through  the  tuber.  The  disease  is  not 
due  to  parasites  and  probably  affects  the  yield  but  little. 
Seed  potatoes  showing  this  disease  should  be  avoided.  An 
Anthracnose  (Colldotrichum)  has  been  described  on  stems. 


Disease  Prevention 

In  general  to  prevent  potato  diseases: 

1.  Plant,  if  possible,  in  uninfested  soil. 

2.  Destroy  disease-bearing  refuse. 

3.  Rotate  crops  judiciously. 

4.  Use  only  seed  free  from  seed-borne  diseases,  i.  e.,  scabs, 
black-scurf,  wilts. 

5.  Disinfect  seed  in  case  such  diseases  as  scab  and  black- 
scurf  are  present,  p.  240. 

6.  Spray  with  4-4-40  Bordeaux  mixture. 

Potato  Spraying  -•"•  -^^ 

As  with  other  crops,  spraying  should  not  be  directed  or 
planned  to  meet  merely  one  of  the  diseases,  but  rather  to 
give  the  plant  the  best  possible  protection  against  all  of  its 
enemies.  The  chief  enemies  to  be  met  by  spraying  are 
early-blight,  late-blight,  and  the  Colorado  beetle  or  "potato 
bug." 


Vegetable  and  Field  Crops 


237 


The  gains  from  spraying  potatoes  with  Bordeaux  mixture 
as  shown  in  trials  at  the  Vermont  Experiment  Station,  begun 
in  1891  by  Jones  and  extending  over  twenty  years,  are  shown 
below : 


Gains  from  the  Use  of   Bordeaux  Mixture  on  Late 
Potatoes 


Sprayed 

Yield  per  Acre 

Planted 

Sprayed 

Not 
Sprayed 

Gain  per  Acre 

White  Star, 
May  — ,  1891 
May  20,  1892 
May  20,  1893 
Apr.  26,  1804 

Mav  20,  1895 
Polaris, 

May  15,  1896 

June    1,  1897 
White  Star, 

May  10,  1898 
Average, 
3  varieties. 

May  18.  1899 

Delaware, 

May  23,  1900 
May  25,  1901 
May  15,  1902 

Green  Mountain, 
May    1,  1903 

Delaware, 

May  25,  1904 
May  15,  1905 

Green  Mountain, 
May  27,  1906 
May    1,  1907 
May  15,  1908 

May  28,  1909 

May    9,    1910 

Aug.  26,  Sept.  8 
July  30,  Aug.  13,  25 
Aug.  1,  16,  29 
June  16,  July  17. 

Aug.  30 
July  25.  Aug.  13,  31 

Aug.  7,  21 

July  27,  Aug.  17,  2S 

July  21,  Aug.  10 

July  26,  Aug.  17, 
Sept.  8 

Aug.  4,  23 
Julv  20,  Aug.  21 
Aug.  1,  20 

Aug.  10 

Aug.  1,  Sept.  1 
Aug.  2,  21 

Aug.  13,  22 

July  16,  25,  Aug.  8,  22 

.June  26,  .July  97 

Aug.  6,  26 
July  12,  23. 
Aug.  6,  27 
July  11,  27,  Aug.  T5, 

23,  30 

313  bu. 
291  bu. 
338  bu. 

323  bu. 
389  bu. 

325  bu. 
151  bu. 

238  bu. 

229  bu. 

285  bu. 

170  bu. 

298  bu. 

361  bu. 

327  bu. 
382  bu. 

1.33  bu. 

171  bu. 

l.'-,6  bu. 
243  bu. 
240  bu. 

24S  bu. 
99  bu. 
114  bu. 

251  bu. 
219  bu. 

2.57  bu. 
80  bu. 

112  bu. 

161  bu. 

225  bu. 
.54  bu. 
164  bu. 

237  bu. 

193  bu. 
221  bu. 

101  bu. 
63  bu. 

65  bu. 

188  bu. 

202  bu. 

65  bu.  or     26% 
192  bu.  or  194% 
224  bu.  or  196% 

72  bu.  or    29% 
170  bu.  or    78% 

68  bu.  or    26% 
71  bu.  or    89% 

126  bu.  or  112% 

68  bu.  or    42% 

60  bu.  or    27% 
116  bu.  or  215% 
1.34  bu.  or    82% 

121  bu.  or    52% 

134  bu.  or    69% 
161  bu.  or    73% 

.32  bu.  or    32% 
108  bu.  or  175% 

91  bu.  or  140% 

.55  bu.  or    29% 

.38  bu.  or     18% 

Avorage  of  20 
years 

268  bu. 

163  bu. 

105  bu.  or    64% 

238 


Diseases  of  Economic  Plants 


Extensive  experiments  were  conducted  for  ten  years  by  the 
New  York  Experiment  Station.  The  following  table  taken 
from  bulletin  349  summarizes  the  results: 


At  Geneva 

At  Riverhead 

Year 

Gain  per  A.  due 

to  spraying 

Every  Two  Wee'KS 

Gain  per  A.  due 
to  spraying 
Three  Times 

Gain  per  A.  due 

to  spraying 

Every  Two  Weeks 

Gain  per  A.  due 
to  spraying 
Three  Times 

1902 

1903 

Bu 
123 . 5 
118 
233 
119 

63 

73 .  (i6 

39 

49  7 

63 

93 

Br,. 

98.5 

88 
191 
107 

32 

44 

29.5 

3S .  7 

22 

40 

Bu. 
45 
56 
96 
82 
53 
31 

15.33 

52 , 5 

25.5 

.5 

Bu 

27 .  66 
39  5 

56  5 

1905 

31    5 

1906 

21   5 

1907 

18 

1908 

10  75 

1909 

28  7 

1911 

11 

Average. ,  . 

97.5 

69 

45.7 

25 

Ten  years  of  business  experiments  made  on  farms  in  order 
to  determine  the  actual  profits  from  spraying  under  farm 
conditions  gave  the  following  results : 


Average 

Average 

Number 

Total 

Total 

Cost 

Average 

Year 

OF  Experi- 

Area 

IN  Yield 

CCST  OF 

PER  Acre 

Net  Profit 

ments 

Sprayed 

Sprayinc, 

FOR  Each 

PER  Acre 

per  Acrf 

Spraying 

.4. 

Bu. 

1903 

6 

61.2 

57 

.fl.OS 

$1.07 

?23.47 

1901 

14 

180 

62  2 

4  98 

.93 

24.86 

1905 

13 

160.7 

46  5 

4  25 

.98 

20.04 

1906 

225  6 

42.6 

5   IS 

.985 

1907 

14 

152.75 

36.8 

5  90 

1    18 

17.07 

1908 

1  i 

200.25 

18.5 

4  30 

.92 

8.53 

1909 

12 

203.14 

24.4 

4.15 

83.5 

9.55 

1910 

12 

218.5 

19.1 

4  04 

90 

4.39 

1911 

U 

161.6 

18  2 

4  87 

96 

8.09 

In  the  Geneva  and  Riverhead  experiments,  rows  sprayed 
three  times  received  Bordeaux  mixture  with  Paris  green 
twice  and  Bordeaux  alone  once,  the  dates  being  July  3,  17, 
and  August  3.  Other  rows  were  sprayed  six  times,  twice  with 
Bordeaux  mixture  and  Paris  green  and  four  times  with 
Bordeaux  alone,  the  dates  being  July  3,  17,  August  3,  18, 
and  September  1,  16.    Still  other  rows  were  not  sprayed  at 


Vegetable  and  Field  Crops  239 

all  with  Bordeaux,  but  were  treated  twice,  July  3  and  20, 
with  Paris  green  in  limewater,  to  control  bugs.  The  Bor- 
deaux mixture  contained  6  pounds  of  copper  sulfate  to  each 
50  gallons  of  water,  and  lime  to  correspond.  Paris  green 
was  used  at  the  rate  of  1  pound  to  50  gallons  of  mixture. 

The  recommendation  of  the  Geneva  Station  is:  "Com- 
mence spraying  when  the  plants  are  six  to  eight  inches  high 
and  repeat  the  treatment  at  intervals  of  10  to  14  days  in 
order  to  keep  the  plants  well  covered  with  Bordeaux  through- 
out the  season.  During  epidemics  of  blight  it  may  be  neces- 
sary to  spray  as  often  as  once  a  week.  Usually  six  applica- 
tions will  be  required.  The  Bordeaux  should  contain  4 
pounds  of  copper  sulfate  to  each  50  gallons  in  the  first  two 
sprayings,  and  6  pounds  to  50  gallons  in  subsequent  spray- 
ings. Whenever  bugs  or  flea  beetles  are  plentiful,  add  one  to 
two  pounds  of  Paris  green  or  two  quarts  of  arsenite  of  soda 
stock  solution  or  three  to  five  pounds  of  arsenate  of  lead  to 
the  quantity  of  Bordeaux  required  to  spray  an  acre. 

"Thoroughness  of  application  is  to  be  desired  at  all  times, 
but  is  especially  important  when  flea  beetles  are  numerous 
or  the  weather  favorable  to  blight.  Using  the  same  quan- 
tity of  Bordeaux,  frequent  light  applications  are  likely  to 
be  more  efi'ective  than  heavier  applications  made  at  long 
intervals. 

"Those  who  wish  to  get  along  with  three  sprayings  should 
postpone  the  first  one  until  there  is  danger  of  injury  from 
bugs  or  flea  beetles,  and  then  spray  thoroughly  with  Bor- 
deaux and  poison.  The  other  two  sprayings  should  like- 
wise be  thorough  and  applied  at  such  times  as  to  keep  the 
foliage  protected  as  much  as  possible  during  the  remainder 
of  the  season.  Very  satisfactory  results  may  be  obtained 
from  three  thorough  sprayings. 

"A  single  spraying  is  better  than  none  and  will  usually 
be  profitable,  but  more  are  better. 

"Except,  perhaps,  on  small  areas,  it  does  not  pay  to 
apply  poison  alone  for  bugs.  When  it  is  necessary  to  fight 
insects,  use  Bordeaux  mixture  and  poison  together." 


240  Diseases  of  Econoinic  Plants 

Arsenical  Injury,  due  to  insecticides,  may  be  avoided  by 
applying  the  arsenicals  with  Hme  or  with  Bordeaux  mixture. 

Potato  seed  disinfection.  —  The  diseases  against  which 
seed  disinfection  is  effective  are  only  those  in  which  the 
fungus  is  superficial  on  the  tuber,  i.  e.,  primarily  against 
common-scab  and  black-scurf,  and  against  these  only  under 
certain  conditions.  Before  disinfecting,  all  tubers  obviously 
bearing  any  other  disease  should  be  discarded,  as  well  as 
tubers  bearing  large  black-scurf  sclerotia  or  deep  scab  pits, 
since  the  treatments  will  not  kill  the  fungi  on  such.  Many 
diseases  of  tubers  cannot  be  detected  until  the  potatoes  are 
cut.  Before  treating,  enough  of  them  should  ])e  examined 
internally  to  give  satisfaction  that  the  lot  is  not  generally 
infected  with  any  internal  disease,  as  for  example,  with 
black-leg  or  wilt.  Disinfection  should  he  done  before  cutting. 
Two  chemicals  are  used  according  to  the  following  formulae : 

1.  Mercuric  chlorid  (corrosive  sublimate).  .    4  oz. 
Water 30  gal. 

2.  Formalin 1  pt. 

Water 30  gal. 

Mercuric  chlorid  must  not  be  brought  in  contact  with 
metal;  is  very  poisonous  to  animals;  deteriorates  rapidly 
with  use,  and  is  more  expensive  than  formalin.  The  formalin 
solution  may  be  used  in  any  kind  of  container;  grows  stronger 
on  evaporation,  and  is  generally  preferable. 

In  either  solution  the  potatoes  are  soaked  for  a  half  hour. 
The  solution  may  be  put  in  a  large  trough,  and  the  potatoes, 
in  crates  or  bags,  set  into  it,  left  the  requisite  time,  then  sub- 
stituted by  another  lot  of  potatoes.  Potatoes  should  be 
dried  immediately  after  treatment.  If  there  is  much  l^lack- 
scurf  present,  and  no  better  seed  are  obtainable,  the  potatoes, 
if  dormant,  i.  e.,  not  sprouted,  may  l)e  soaked  for  two  hours 
in  mercin-ic  chlorid  solution.  With  sprouted  stock  the  mer- 
curic chlorid  is  more  injurious  than  the  formalin,  but  the 
formalin  is  not  effective  against  heavy  infection  of  black-scurf. 


Vegetable  and  Field  Crops  241 

PUMPKIN.    See  cucumber. 
RADISH.    See  cabbage. 
RAPE.    See  cabbage. 

RHUBARB 

Anthracnose  '-'"  {C olletotrichum erumpens Sa,cc.) .  —Rotted, 
sunken,  soft  spots,  often  several  centimeters  long,  are  pro- 
duced on  the  petioles,  and  are  thickly  set  in  the  older  portions 
with  black  acervuli.  Though  reported  as  yet  only  from 
Illinois,  the  disease  is  probably  widespread,  and  causes 
considerable  loss  in  the  field,  and  additional  loss  in  shipment. 

Leaf-spot '-^^  {Phyllosticta  sirarninella  Bres.).  —  Irregular, 
brownish,  diseased  spots,  often  several  centimeters  in  diam- 
eter, occur  on  the  leaf  blade  and  bear  numerous,  minute, 
black  p3^cnidia.    Older  spots  become  torn  and  ragged. 

Crown-rot. — This  soft  rot  of  crown  and  petiole,  probably 
due  to  bacteria,  has  caused  large  loss  in  southern  Illinois. 

ROSELLE    (Hibiscus  sabdariffn) 

Powdery-mildew  {Microsphcera  euphorbice  B.  &  C, 
Oidiiun). — This  mildew  of  characteristic  white,  flour-like, 
circular  patches  has  been  noted  in  Florida. 

Flowers  of  sulfur  has  proved  effective  in  preventing  its 
spread. 

RUTABAGA.    See  cabbage. 


SALSIFY 

White-rust  {Albugo  tragopogonis  (DC.)  Gray).  —  White, 
rustlike  blisters  (sori)  upon  the  leaf  indicate  this  disease. 
In  late  stages  of  the  disease  the  leaf,  near  the  sori,  blackens 
and  withers,  often  tearing  lengthwise. 

Soft-rot.  —  A  soft-rot  of  the  loots,  resulting  in  loss  of 
green  color  and  prostration  of  the  plants,  is  attributed  to 


242 


Diseases  of  Economic  Plants 


i:)acteria.  The  slimy,  offensive  decay  usually  begins  at  the 
lower  end  of  the  main  root  and  progresses  upward.  See 
carrot  soft-rot. 

Rust  (Puccinia  tragopogonis  (Pers.)  Cda.).  —  This  true 
rust  is  of  somewhat  general  distribution,  but 
is  not  harmful. 

Powdery-mildew  (Erysiphe  sps.)  is  com- 
mon, but  not  serious.  Southern-blight  (Scle- 
rolium)  is  injurious  in  the  South. 

SPINACH  "■•** 

Blight.-'^'^ — This  is  the  most  destructive 
spinach  disease,  causing  a  loss  in  eastern 
Virginia  estimated  between  S200,000  and 
$400,000  annually.  The  diseased  leaves  are 
mottled  and  deformed,  and  the  plants 
stunted.  In  general,  the  symptoms  are  much 
as  in  the  mosaics  with  the  exception  that 
the  plants  are  eventually  killed.  The  disease 
is  due  to  a  virus,  and  can  be  artificially 
transmitted  from  plant  to  plant.  In  nature, 
infection  seems  to  be  carried  by  plant  lice 
(aphids),  and  not  to  reside  in  the  soil  or  to 
be  carried  by  the  seed.  Spraying  to  kill  the 
plant  lice  may  be  the  means  of  conquering 
this  trouble. 

Anthracnose  {Colletotrichum  spinadoe  E.  & 
H.).  —  Blotches  appear  upon  the  leaves,  first 

Fig.  132.- White-  as  small,  moist,  watery  areas,  associated  with 

rust  upon  sal-  slight  local  wilting,  followed  soon  by  the  ap- 

Aft     h'^  1]  ^    pearance  upon  either  side  of  the  leaf  of  small, 

brown  acervuli.    The  spots  then  change  to 

gray  and  dry  up.    The  disease  spreads  rapidly  from  plant  to 

plant  and  is  very  destructive  both  under  glass  and  in  the 

open,  rendering  the  plant  unfit  for  use. 

White-smut    (Entijloma    ellisii    Hal.).  —  The    attacked 

plants  are  unmarketable,  due  to  lack  of  uniform  green  color 


Vegetable  and  Field  Crops 


243 


and  the  presence  of  pale  bleached  spots  upon  the  foliage. 
These  spots  are  not  definitely  limited,  nor  does  the  tissue  die 
as  it  does  in  the  case  of  other  spinach  leaf  spots. 

Black-mold  {Cladosporium  macrocarpum  Preuss)  develops 
primarily  upon  old  leaves,  and 
renders  the  plant  unsalable.  The 
spots  are  distinguishable  from  all 
other  spinach  spot  diseases  by 
their  irregularity,  indefiniteness, 
and  color. 

To  control  the  three  latter 
spinach  diseases,  it  is  well  to  burn 
diseased  refuse,  practice  I'otation, 
and  employ  preventive  sprays 
when  the  plants  are  young. 
Spraying  the  edible  leaves  as  the 
plants  approach  maturity  injures 
the  sale  and  is  not  permissible. 

Leaf-spot  (Heterosporium  va- 
riahile  Cke.).  — -This  disease  was 
especially  injurious  to  spinach  in 
eastern  Virginia  during  the  win- 
ter of  1908-1909,  and  has  also 
been  noted  in  Connecticut,  It 
appears  early  in  January  and 
continues  to  increase  until  the 
spinach  season  is  over.  Numer- 
ous leaf  spots  are  produced,  at 

first  brown,  later  sooty,  as  the  conidiophores  and  conidia 
of  the  fungus  develop.  The  older  leaves  usually  show  more 
injury  than  the  younger,  but  at  times  all  leaves  are  seriously 
affected.  The  presence  of  the  fungus  renders  the  leaves 
unsalable,  and  much  additional  labor  is  required  at  harvest 
time  to  trim  off  the  injured  leaves. 

The  disease  does  not  seem  capable  of  attacking  healthy, 
vigorous  plants,  but  usually  follows  injuries  produced  by 
some  other  agencies.    In  Virginia  it  has  been  found  to  follow 


Fig.  133.  —  Spinach  leaf 
spotted  by  Heterosporium. 
After  Reed. 


244  Diseases  of  Econoinic  Plants 

the  injuries  produced  by  Peronospora.  Injuries  produced  by 
cold  weather,  prolonged  rains,  insects,  etc.,  undoubtedly 
afford  weak  points  where  infection  may  begin. 

The  best  preventive  measures  are  to  follow  general  h}^- 
gienic  precautions,  rake  up  and  destroy  all  dead  and  diseased 
leaves,  keep  the  injuries  from  insects  and  other  fungi  at  a 
minimum,  and  rotate  crops  as  frequently  as  possible. 

Minor  Diseases 

Downy-mildew  {Peronospora  effusa  (Grev.)  Rl^h.).  — 
Gray  to  slightly  violet,  downy  spots  upon  the  lower  sur- 
faces of  leaves,  accompanied  by  pale  yellow  spots  upon  the 
corresponding  upper  surfaces,  indicate  downy-mildew.  The 
disease  in  its  habit  and  damage  resembles  that  of  the  grape, 
p.  122.  Serious  loss  is  reported  from  New  Mexico  and 
Virginia. 

Leaf -blight  {Phyllosticta  chenopodii  Sacc.)  affects  the 
leaves,  especially  at  their  bases,  producing  spots  which  bear 
minute  pycnidia.  Leaf-spot  {Cercospora  bcticola  Sacc.)  often 
ruins  crops  by  yellowing  and  dwarfing  the  plants,  thus  ren- 
dering them  worthless  for  market.  Soft-rot  {Bacillus  carot- 
ovorus)  occurs  on  spinach  in  shipment. 

SQUASH.    See  p.  178. 

SUGAR  CANE  i''^  '^-^^ 

Red-rot  {Colletoirichum).  —  The  first  external  evidences  of 
disease  are  drooping,  withering,  and  yellowing  of  the  upper 
leaves,  followed  by  wilting  of  the  entire  crown.  Finally,  the 
whole  stool  dies.  In  less  severe  cases  buds  die,  and  dead, 
black  areas  extend  out  from  the  nodes.  The  veins  running 
lengthwise  within  the  stems  are  reddened.  Uncertainty 
exists  as  to  identity  of  the  causal  fungus.  The  disease  is 
one  of  the  most  serious  affecting  sugar-cane.  Only  healthy 
stock  should  be  used  in  propagation,  and  diseased  refuse 
should  be  destroved. 


Vegetable  and  Field  Crops  245 

Rind-disease  {Trichosphnace  sacchari  Mass.).  —  This 
stem  disease  is  first  indicated  by  yellowing  and  drying  of  the 
leaves,  often  followed  by  death  of  the  plant.  The  nodes  are 
frequently  discolored  or  black.  In  late  stages  black  pycnidia 
appear  on  the  diseased  surface.  Diseased  refuse  should  be 
burned  and  cuttings  should  be  disinfected  by  dipping  in 
Bordeaux  mixture. 

Pineapple-disease  {Thielnviopsis  paradoxa  v.  Hohn.). — 
This  disease  originates  in  cuttings  and  derives  its  name  from 
the  odor  of  the  affected  stems.  The  fungus,  which  is  a 
wound  parasite,  enters  through  the  ends  of  cuttings  and 
may  prevent  their  germination,  or  so  retard  growth  that 
worthless  plants  develop.  Dipping  the  cut  ends  in  Bordeaux 
mixture  lessens  infection. 

Ring-spot  (Leptosphceria  sacchari  v.  B.  d.  H.). — Oval, 
gray  spots,  3-5  x  5-15  mm.,  surrounded  by  narrow  brown 
rings,  develop  in  the  leaves,  and  bear  minute,  l)lack  peri- 
thecia. 

Leaf-spot  {Cercospora  longipes  Butler).  —  Narrow,  oval, 
brown  spots,  about  2  mm.  in  diameter,  surrounded  by  a 
yellow  zone,  occur. 

Cacao-disease  {Diplodia  cacaoicola  Hen.).  —  This  is  caused 
by  a  fungus  that  also  grows  on  cacao.  It  causes  the  canes 
to  wrinkle. 

Root-rot.  This,  one  of  the  most  troublesome  of  cane 
diseases,  is  due  to  various  fungi,  one  of  which  is  a  stink-horn 
(Phallus),  another  Marasmius  sacchari,  Wak.,  })oth  of  which 
can  be  recognized  in  late  stages  by  the  sporophores  of  the 
fungi.  Proper  drainage  and  cultivation,  the  use  of  immune 
varieties  and  healthy  stock,  the  destruction  of  infected 
refuse,  and  rotation  of  crops  are  helpful. 

SWEET  CORN.    See  p.  283. 

SWEET  POTATO  -^^  ^^^ 

Soft-rot  ^"^  {Fhizopus  nigricans  Ehr.).  —  The  most  prom- 
inent soft-rot  of  the  sweet  potato,  the  only  one  that  is  com- 


246 


Diseases  of  Economic  Plants 


monly  met,  may  be  recognized  by  the  soft,  wrinkled  condi- 
tion of  the  potato,  its  sweetish  odor,  and  usually  by  the 
presence  of  a  white,  later  black,  growth  of  mold,  appearing 
through  the  skin  of  the  rotted  portion  at  points  of  rupture. 
The  decay  most  often  begins  at  one  end  and  passes  rapidly 
through  the  root,  ])ut  it  may  start  at  a  wound  upon  any 


^&4lx 

1 

^^T^'^jOr^X&i*' 

^^gi^^^^^S 

i 

^ 

' 

f'Ki.  134.  —  Sweet  potato  soft-rot. 


part  of  the  potato.  It  progresses  with  such  rapidity  that  the 
whole  potato  may  give  way  in  a  few  days  after  infection. 
Other  tubers,  if  they  have  broken  surfaces  or  wounds  and 
lie  in  contact  with  affected  ones,  will  also  become  infected. 
The  rotten  roots  are  therefore  often  found  in  groups  through- 
out the  pile.  This  rot  is  sometimes  found  in  the  field,  but  is 
not  usually  destructive  until  after  digging.  The  loss  in  the 
United  States  in  1917  is  estimated  at  about  5,000,000  bu. 


Vegetable  and  Field  Crops  247 

Normally  it  cannot  enter  a  sound  potato;  a  wound  must 
furnish  a  passageway.  Therefore  all  wounded  roots  should 
be  laid  aside  for  immediate  consumption,  and  pnly  sound 
roots  put  in  storage. 

Potatoes  for  storage  should  be  fully  matured,  carefully 
handled  to  avoid  bruising,  thoroughly  cured,  and  kept  at 
uniform  temperature,  26°  to  29°  C.  (80°  to  85°  F.),  while 
curing,  and  at  12°  C.  (55°  F.)  after  curing.  Properly  ven- 
tilated storage  houses  should  l)e  built  when  possible.  Kiln 
drying  at  29°  to  35°  C.  (85°  to  95°  F.)  for  10  to  15  days  is  a 
good  practice. 

It  is  well  to  destroy  all  infective  material,  rotten  roots, 
etc.,  in  or  near  the  stoi-age  place,  and  if  the  house  has  been 
infested,  to  spraA^  its  walls  and  floors  thoroughly  with  a  good 
disinfectant,  such  as  Bordeaux  mixture  or  formalin. 

Black-rot  {Sphwronema  fimhriatum  (E.  &  H.)  Sacc).  — 
This  is  among  the  most  destructive  of  all  sweet  potato 
decays,  causing  much  loss  in  storage  as  well  as  in  the  field. 
It  is  said  to  equal  in  damage  that  of  all  other  sweet  potato 
diseases  combined.  Infected  potatoes  are  bitter  and  worth- 
less. Black-rot  has  been  reported  from  nearly  all  states  that 
raise  sweet  potatoes,  also  from  the  West  Indies  and  New 
Zealand. 

The  rot  may  be  known  by  its  dark  brown  to  l^lack,  irregu- 
lar patches  upon  the  potato  surface.  These  begin  as  points 
and  gradually  extend  in  all  directions,  involving  the  whole 
root.  Older  spots,  2-5  cm.  across,  often  break  or  crack 
irregularly  near  the  center.  This  decay  differs  from  the 
soft-rot  in  that  the  spots  are  dry  and  hard  and  that  it  is 
present  upon  the  roots  before  digging.  With  a  hand  lens, 
very  small,  hairlike,  black  structures,  1  mm.  high,  are  seen 
studding  the  centers  of  the  diseased  areas.  These  are  the 
beaks  of  the  pycnidia  of  the  causal  fungus. 

Upon  young  sprouts  before  they  are  set  out  the  disease 
causes  black,  dead  patches,  especially  at  the  base  of  the 
shoot  or  even  upon  the  young  leaves.  The  wood  of  the  stem 
may  be  browned.     Such  sprouts  result  in  enfeebled  plants 


248 


Diseases  of  Economic  Plants 


with  diseased  roots.  The  fungus  discharges  myriads  of 
spores  into  the  soil.  This  disease  thus  falls  under  the  general 
class  of  soil  diseases. 

In  addition  to  the  suggestions  given  on  page  26,  especial 
precaution  should  be  exercised  to 
avoid  sets  already  infected.  Badly 
diseased  shoots  are  easily  recognized, 
hut  the  closest  scrutiny  is  needed  to 
cull  out  those  only  slightly  affected. 
Al)Ove  all,  infested  seed  beds  should 
be  avoided,  and  no  infected  potatoes 
should  be  used  for  growing  sets.  Crop 
rotation  should  be  practiced,  and 
every  precaution  taken  to  get  the 
jilants  well  established  in  the  field. 
A  strong,  well-started  plant  will  often 
r(>sist  the  disease  where  a  weak  plant 
would  succumb.  Waite  ^^^  says :  "The 
best  remedy  is  to  use  slip  seed.  It  is 
advisable  to  grow  the  crop  of  vine 
cuttings  on  new  land  which  is  not  in- 
fested or  on  land  which  has  never 
gi-own  sweet  potatoes,  thus  making 
an  absolutely  clean  start  even  though 
the  vine  cuttings  are  taken  from  an 
infected  crop." 

Root-rot  '^^'   (Plenodomus   destruens 
Hart.).  —  Small  brown  or  black  spots 
appear  on  the  stem  near  the  soil  line, 
and  eventually  girdle  the  plant,  which 
soon  wilts.     In  some  regions  of  Ohio, 
Virginia,  and  Iowa,  losses  of  50  per  cent 
occur,  but  the  disease  is  not  so  widely 
distributed  as  those  mentioned  above. 
Texas  root-rot  {Ozonium).  —  A  firm,  brown  rot  is  pro- 
duced on  th(>  ]X)tatoes.    Loss  as  high  as  90  per  cent  is  occa- 
sional.   Rotation  involving  cereals  should  be  adopted. 


Fig.  135.  —  Black-rot  of 
sweet  potato.    Original. 


Vegetable  and  Field  Crops 


249 


// 


kf.f- 


Soil-rot  301. 303  (Cystospora  hatatce  (E.  &  H.)  Ell.).  — The 
loss  from  this  rot  is  sometimes  almost  total.  Due  to  soil 
infestation  the  raising  of  the  crop  is  pro- 
hibited for  several  years. 

The  roots  are  attacked  when  quite 
small,  sometimes  over  the  whole  surface. 
The  part  infected  ceases  to  grow,  while 
adjoining  parts  enlarge.  This  results  in  a 
condition  such  as  that  shown  in  Fig.  136. 
The  smallest  rootlets  are  the  points  of 
attack,  thence  the  disease  proceeds  to 
the  potato  and  causes  the  surface  spots 
as  seen  in  the  illustration. 

The  chief  loss  is  in  the  cessation  of 
growth.  In  badly  infested  fields  no  po- 
tatoes of  marketable  size  mature,  and 
the  crop  is  not  worth  harvesting. 

Long  rotation  to  avoid  placing  sweet 
potatoes  upon  infested  soil  is  advised. 
Halsted  showed  that  soil-rot,  even  upon 
land  badly  infested  with  the  fungus,  can 
be  controlled  by  sulfur  and  kainit;  400 
pounds  of  each  applied  to  the  soil  gave 
the  best  results.  Treated  plats  gave  60 
bushels  of  clean  potatoes  as  contrasted     /C"'' '.  .  ,^^^M 

with  5  bushels  for  the  untreated  plat.         ^-'f'-^ 

Wilt,  stem-rot  (Fusarium  sps.).  —  In    W"}"*'^^^ 
this  disease,  prevalent  from  the  Atlantic    L     /v\f 
to  Kansas,  the  leaves  turn  pale  yellow     F-^ . 
and  wilt;  the  stem  is  blackened  within,       ^^ 
and,   later,  ruptures.     The   whole   vine 
dies  unless  supported  by  roots  at  some 
other  point.    Following  the  death  of  the 
original  stem,  the  portion  of  the  root  still 

alive  throws  out  a  fresh  growth  of  short       ^  ^^  .. 

stems  and  leaves  near  the  center  of  the    j.^^.  ^j  ^^^^^  potato. 
hill.     Such  efforts  at  recovery  are  inef-    After  Halsted. 


250  Diseases  of  Economic  Plants 

fectual.  Losses  range  anywhere  from  10  to  95  per  cent  of 
the  crop,  and  the  total  annual  loss  is  at  least  three-quarters 
of  a  million  dollars.  Healthy  potatoes  must  be  used  for 
seed;  the  hotbed  should  occupy  uninfested  soil,  and  rotation 
should  be  practiced.  The  suggestions  given  under  soil  dis- 
eases apply  here. 

Minor  diseases 

Dry-rot  {Diaporthe  batalatis  H.  &  F.,  Photnopsis) .  —  The 
affected  part,  often  the  upper  end  of  the  potato,  becomes 
dry,  wrinkled,  and  covered  with  numerous  pycnidia,  the 
flesh  within  changing  to  an  almost  powdery  condition. 
Affected  potatoes  should  be  destroyed.  Java  dry-rot ''"'' 
(Diplodia  iiibericola  (E.  &  E.)  Taub.).  ^  The  potatoes  show 
dark,  shriveled  patches  with  scattered  pycnidia.  The  inner 
tissue  is  brittle  and  black.  Scurf  ^'^-^  (Monilochcetes  infuscans 
E.  &  H.).  —  A  brown  or  rusty  coat  often  forms  over  the 
whole  potato.  It  causes  no  decay,  but  does  result  in  shrink- 
ing, loss  of  volume,  and  vmsightliness,  which  reduces  the 
money  value  of  the  crop.  Blue-mold  rot  (Penicillium  expan- 
sum). — ^  The  diseased  parts,  which  may  involve  the  whole 
potato,  are  of  almost  chalky  color  and  consistency,  dry,  and 
inoffensive  in  character. 

White-rust  {Albugo  ipomoece-pandurana;  (Schw.)  Swingle). 
—  White,  glistening  sori,  1  nun.  or  so  in  diameter,  appear 
upon  the  under  sides  of  the  leaves  and  upon  the  stems. 
These  rupture  and  set  loose  a  mass  of  powdery,  snow-white 
spores.  The  tissue  surrounding  the  sorus  is  pale,  or  yellow,  as 
seen  from  the  opposite  side  of  the  leaf.  Later,  brown  patches 
result. 

Leaf-blight  {Phijllosticta  batatas  Cke.).  — Spots  of  brown, 
dead  tissue  from  1-10  nun.  in  diameter,  round  or  angular, 
are  frecjuent  upon  the  leaf.  Thej"  are  very  definitely  bordered 
by  a  dark  Ijand,  and  bear  numerous  pycnidia,  visible  to  the 
naked  eye.  In  many  instances  these  spots  become  so  nu- 
merous as  to  cause  the  whole  leaf  to  yellow  and  fall,  and  thus 
reduce  the  crop. 


Vegetable  and  Field  Crops  251 

Leaf-spot  (Septoria  bataticola  Taub.)  is  similar  to  leaf- 
blight,  lint  with  smaller  spots.  Charcoal-rot  (Sderotium 
bataticola  Taub.)  is  similar  in  general  character  to  Java  dry- 
rot.  Rust  {Coleosporium  ipomcem  (Schw.)  Burr.).  —  The 
alternate  host  is  the  pine.  Rust  is  injurious  in  the  tropics. 
Trichoderma-rot  (Trichodcrma  koningi  Oud.)  and  Root-knot 
(nematodes)  do  some  damage. 

TEA  '''^ 

The  diseases  of  the  tea  plant  are  mmierous  and  destructive, 
but  since  the  crop  is  little  grown  in  the  continental  United 
States,  they  may  be  enumerated,  merely,  as  follows:  Gray- 
blight  (Pestalozzia)  and  Brown-blight  (Colletotrichum)  spot- 
ting the  leaves ;  Blister-blight  (Exobasidium) ;  Thread-blight 
(Stilbum)  which  kills  l)ranches  or  even  the  entire  plant; 
Copper-blight  (Lcestadia)  causing  copper-colored  leaf-spots; 
Red-rust  due  to  the  alga,  Cephaleurous,  Canker  due  to 
Nectria;  Blight  due  to  Marasmius. 

TOBACCO. 

Root-rot  '''■  '^'  {Thielavia  basicola  (B.  &  Br.)  Zopf.).  — 
Known  in  Europe  since  1897,  this  disease  was  first  reported  in 
the  United  States,  in  1904,  as  occurring  upon  tobacco, 
though  it  has  probably  been  long  prevalent  in  tobacco  sec- 
tions. It  has  l)een  noted  upon  other  hosts;  namely,  violets 
in  Connecticut,  Maryland,  and  District  of  Columbia; 
ginseng  in  Ohio  and  New  York;  also  upon  begonia,  catalpa, 
and  clover.  Upon  tobacco  it  is  now  known  in  Ohio,  Con- 
necticut, Kentucky,  and  North  Carolina,  and  its  territory  is 
increasing  yearly.    See  also  p.  23. 

Root-rot  in  the  seed  bed  often  causes  the  entire  crop  of 
seedlings  to  be  discarded,  delaying  planting  or  compelling 
a  change  of  crop.  In  the  field  the  loss  sometimes  amounts 
to  25  per  cent. 

The  disease  is  recognized  l)y  the  black  decay  upon  the 
roots,  sometimes  by  a  cracking  and  deformation  on  the  stem 


252 


Diseases  of  Economic  Plants 


just  above  the  roots  antl  the  failure  of  the  plant  to  develop 
normally. 

Damping-off  due  to  Thielavia  or  other  fungi  may  occur  in 
seed  beds.     The  plants  are  attacked  when  very  young,  and 


Fig.  137. ^Tobacco  roots  showing  effect  of  root-rot. 
After  Gilbert. 


death  may  result  before  they  attain  a  height  of  more  than 
5-10  mm.  In  other  cases  of  milder  attack  the  roots  alone  are 
invaded  and  the  plants  stunted.     The  tips  of  the  rootlets 


Vegetable  and  Field  Crops  253 

become  brown  or  black,  and  the  entire  root  system  is  in- 
volved later.  The  decayed  roots  are  brittle  and  break 
easily.  Numerous  lateral  rootlets  are  put  out  to  replace 
them,  but  these  also  succumb  sooner  or  later.  The  leaves  of 
diseased  seedlings  on  rich  soil  are  usually  abnormally  dark 
green.  They  may,  however,  in  poor  soil  be  of  a  sickly  yellow 
color. 

In  the  field  the  diseased  seedlings  may  remain  without 
growing  for  weeks;  some  yellowing,  wilting,  and  dying. 
Others  in  light  soil  may  survive  and  yield  a  fair,  but  late, 
crop;  in  heavy  soil  few  survive  to  be  of  value.  When  large 
roots  are  attacked,  the  effect  is  generally  limited  to  the  outer 
surface,  where  a  brownish,  scurvy  appearance  is  produced. 

Sick  plants  in  uninfested  soil  or  healthy  plants  set  in  in- 
fested soil  result  in  diseased  crops,  and  the  development  of 
the  disease  when  the  causal  fungus  is  present  is  favored  by 
alkaline  fertilizers. 

To  avoid  loss,  only  uninfected  plants  from  a  clean  seed 
bed  should  be  used.  A  seed  bed  can  be  rendered  safe  and 
so  maintained  by  disinfection,  by  the  means  suggested 
on  page  460,  selecting  the  method  best  applicable  to  the 
conditions.  Surface  firing  is  the  method  most  widely  used  in 
connection  with  the  tobacco  crop.  Formalin  and  steam  have 
also  proved  efficient  in  many  instances. 

The  following  measures  conduce  to  reduction,  though 
not  to  complete  eradication  of  the  disease:  the  use  of  light 
rather  than  heavy  soils  for  the  seed  bed ;  avoidance  of  excess 
of  water  or  fertilizer;  the  use  of  a  new  bed  each  year;  avoid- 
ance of  too  heavy  seeding.  Infested  fields  should  be  given  a 
rotation  of  nonsusceptible  crops.  A  strain  of  white  Burley 
has  been  developed  to  a  state  of  high  resistance. 

Granville-wilt  -°'  ^''^'  ^'^^'  ^^^'  ^"^^  (Pseudomonas  solanacearum 
(EFS.)  ).  — This  wilt  was  first  noted  in  print  in  1903 
though  known  to  tobacco  growers  in  Granville  County,  N.  C, 
as  early  as  1881.  It  takes  possession  of  the  soil,  prohibiting 
successful  tol)acco  culture  in  succeeding  years,  and  in  sections 
where  tobacco  is  the  chief,  possibly  the  only  profitable  money 


254 


Diseases  of  Economic  Plants 


Vegetable  and  Field  Crops' 


255 


crop,  the  advent  of  this  disease  has  caused  great  depreciation 
in  farm  values. 


Fig.  139.  —  Tobacco  plant  in  early  stage  of  the  Granville- 
wilt.    Original. 


The  wilt  is  now  known  in  North  Carolina,  Florida,  Georgia, 
possibly  Connecticut,  and  what  appears  to  be  the  same 
disease  has  been  described  in  Cuba,  Porto  Rico,  France,  the 
Dutch  East  Indies,  and  Japan. 


256 


Diseases  of  Economic  Plants 


The  first  indication  of  the  disease  is  given  through  the  leaves, 
which  droop,  becoming  soft  and  flabby  as  though  suffering 
from  want  of  water,  the  leaves  remaining  green.  A  typical  case 
is  shown  in  Fig.  139.    Frequently  the  leaves  on  one  side  of  the 

plant  succumb  earlier 
than  those  on  the 
other  side,  and  even  a 
single  leaf  may  show 
one-sided  infection. 
The  wilted  leaves  dry 
up,  and  eventually 
leaves  and  stalk  die, 
though  the  stalk  re- 
mains standing  with 
its  dead  leaves  still 
clinging  to  it. 

At  the  stage  of  earl- 
iest wilting  a  section 
across  the  stem  shows 
a  yellowish  discolora- 
tion of  the  woody  por- 
tion. In  more  ad- 
vanced stages,  or  in 
sections  taken  lower 
on  the  stem,  the  wood 
is  found  to  be  pene- 
trated longitudinally 
by  black  streaks. 
When  all  the  leaves 
are  wilted,  the  wood  and  bark  at  the  base  of  the  plant  are 
blackened  and  the  pith  decayed,  leaving  the  stem  hollow  or 
filled  with  a  soft,  rotten  residue.  If  a  badly  diseased  plant 
is  cut  off  near  the  ground,  a  dirty,  yellowish,  viscous  exu- 
date issues  from  the  cut  wood. 

The  root  is  the  seat  of  the  original  infection,  and  any 
plant  which  shows  symptoms  in  its  foliage  possesses  roots 
already  in  a  pionounced  stage  of  decay.     In  early  stages 


Fig.  140.  —  Tobacco  plant  in  late  stages  of 
the  Granville-wilt.    Original. 


Vegetable  and  Field  Crops  257 

one  root  or  more  may  be  diseased;  in  later  stages  all 
succumb. 

In  a  series  of  rotation  tests,  planned  and  inaugurated  by 
the  author, ^^^  it  was  found  that  growing  corn,  wheat,  cow- 
peas,  clover,  and  mixed  grasses,  either  singly  or  in  rotation  for 
a  period  of  five  years  on  badly  diseased  soil,  reduced  the  loss 
from  wilt  to  an  almost  negligible  quantity. 

The  means  by  which  this  disease  spreads  from  field  to 
field,  and  methods  to  prevent  such  spreading,  are  adequately 
discussed  under  soil  diseases,  p.  26. 

A  similar  wilt,  but  due  to  a  Fusarium,  has  been  reported 
from  Maryland. 

Wildfire  ^""^^  ""''  {Pseudomonas  tabacum  (W.  &  F.)). — 
A  bacterial  leaf-spot,  first  noticed  in  1917,  is  widespread 
in  North  Carolina,  Virginia,  and  occurs  also  in  Wiscon- 
sin. Loss  of  $100  per  acre  for  entire  crops  is  commonly 
reported.  The  spot  is  2-3  cm.  in  diameter,  often  concen- 
trically marked,  and  has  a  translucent  border  surrounded  bj'  a 
chlorotic  halo.  Another  bacterial  leaf-spot  known  as  An- 
gular leaf-spot  (Ps.  angulatum  (F.  &  M.))  was  also  described 
in  1917  as  destructive  in  Virginia.  The  spots  are  angular  and 
are  not  surrounded  by  the  halo  common  in  "wildfire." 

Leaf-spot ''*°^  {Cercospora  nicotiance  E.  &  E.). — This  dis- 
ease, most  abundant  upon  the  lower  leaves,  appears  as  brown, 
circular  spots  from  the  size  of  a  pinhead  to  a  centimeter  or 
more  in  diameter.  Older  spots  bear  white  centers  bordered  by 
a  darker,  raised  line,  and  the  centers  often  fall  away,  leaving  ir- 
regular holes.  The  whole  leaf  yellows  and  ripens  prematurely. 

The  disease  was  first  described  by  Sturgis  from  specimens 
sent  from  South  Carolina,  where  it  was  destructive,  prac- 
tically ruining  the  crop.  A  damage  of  SIOOO  to  one  crop 
alone  was  noted.  The  use  of  Bordeaux  mixture  early  in  the 
season  is  permissible  and  advantageous. 

Bed-rot  iCorticium  vagum) .  —  Damping-off  and  rot  of 
seedlings  occur  in  the  seed  bed.  The  causal  fungus  may  often 
be  seen  as  spots  of  web-like  white  mold  upon  the  ground 
around  the  affected  plants.     The  general  characters  and 


258 


Diseases  of  Economic  Plants 


prophylaxis  are  discussed  under  damping-off,  p.  19.     Seed 

beds  known  to  be  diseased 
should  be  avoided  unless 
previously  disinfected. 

Drop  ^^^  {Sclerotinia  liber- 
tiana).  —  Damping-off  due 
to  Sclerotinia  is  reported  as 
a  common  trouble  in  seed 
beds.  The  injury  to  the 
plant  is  similar  to  that  of  the 
usual  damping-off  while  the 
fungvis  presents  the  charac- 
ters described  under  lettuce- 
drop.  Young  plants  are 
killed ;  older  plants  may  sur- 
vive, and  if  set  in  the  field, 
develop  poorlv. 

Mosaic.  ^^-  ^'^  —  Wher- 
ever tobacco  is  grown  the 
mosaic  is  very  widely  dis- 
tributed and  destructive. 
Depreciation  of  $50,000  in 
quality  was  attributed  to  it 
in  Ohio  in  1905.  It  pro- 
duces a  mottled  appearance 
of  the  leaves  due  to  varia- 
tion in  texture  and  green- 
ness ;  parts  of  the  leaf  show- 
ing full  green  and  normal 
thickness,  other  spots  pale 
oi-  yellowish  green,  and  thin. 
Accompanying  these  signs 
are  distortions  due  to  un- 
equal growth,  wrinkled  or 
curled  leaves,  and  leaves  of 

one-sided  growth.    Slightly  affected  leaves  are  depreciated  in 

value ;  badly  diseased  leaves  are  worthless. 


Fig.  141.  —  Tobacco  leaf  showing 
leaf-spot.  After  Conn.  Agr. 
Exp.  Sta. 


Vegetable  and  Field  Crops  259 

The  cause  of  mosaic  is  unknown,  but  it  has  been  repeatedly 
shown  experimentally  that  it  can  be  communicated  from 
plant  to  plant  by  first  touching  a  diseased  plant  and  later 
touching  a  healthy  one.  The  disease  then  appears  within 
six  to  fourteen  days.  Thus  the  disease  is  spread  largely  by 
topping.  In  nature  it  is  probably  spread  by  insects.  The 
virus  appears  to  be  present  in  all  parts  of  an  affected  plant, 
even  in  the  trichomes,  and,  when  inoculated  locally,  spreads 
rapidly  throughout  the  plant,  though  the  disease  is  not 
transmitted  to  the  offspring  through  seed  from  diseased 
capsules.  Tomatoes,  petunia,  physalis,  datura,  solanum 
(but  not  the  potato),  and  pepper  are  susceptible  to  inocula- 
tion from  tobacco  plants. 

The  seed  bed  should  be  either  new  or  thoroughly  disin- 
fected by  steam  or  firing,  and  no  tobacco  refuse  or  tobacco 
water  used  on  it.  Diseased  seedlings  in  the  bed,  if  any  ap- 
pear, should  be  destroyed.  It  is  well  to  top,  worm,  and 
sucker  the  healthy  and  sick  plants  separately,  on  different 
days,  thoroughly  washing  the  hands  with  soap  and  water 
before  passing  from  the  diseased  to  healthy  plants. 

Orobanche.  —  This  is  a  true  flowering  plant,  whicli  draws 
its  noinishment  from  the  roots  of  the  tobacco  plant  to  which 
it  is  attached.  The  orobanche  occurs  in  small  clusters,  its 
stalks  are  from  1-4  dm.  tall,  and  entirely  devoid  of  green 
color. 

They  should  be  pulled  and  burned  before  they  produce 
seed.    Root-knot  (nematodes),  see  p.  24. 

Curing-house  "  diseases."  —  When  tobacco  is  cured  by 
natural  heat,  various  rots  may  occur.  Among  these  are: 
Stem-rot,  due  to  various  fungi ;  Pole-rot,  consisting  of  small, 
blackened  areas  upon  the  leaf,  limited  at  first  to  the  regions 
near  the  veins.  These  spots  may  enlarge  within  two  days  to 
cover  whole  leaves,  and  the  contents  of  the  entire  barn  may 
become  worthless,  the  leaf  having  become  so  wet  and  soft 
as  to  readily  fall  apart.  The  cause  of  these  rots  is  not  cer- 
tainly known;  indeed  there  ma>'  be  several  separate  or- 
ganisms, each  capable  of  inducing  such  rot. 


260  Diseases  of  Economic  Plants 

These  troubles  can  largely  be  controlled  by  proper  regula- 
tion of  the  moisture  and  temperature  conditions,  ?.  e.,  by 
building  such  barns  that  outside  air,  when  too  damp,  can  be 
excluded,  and  yet  with  proper  provision  for  ventilation  to 
carry  off  the  moisture  from  the  drying  tobacco. 

Wet-butts  is  due  to  freezing  before  curing  is  complete; 
White- vein  to  rapid  drying;  Black-rot  (Sterigmatocystis 
nigra  v.  Tieg.)  occurs  during  the  sweating,  the  tobacco  turn- 
ing black  and  losing  its  proper  texture.  It  is  brought  about 
by  too  high  moisture  content. 

TOMATO.^'^  ^^^ 

Bacterial  Wilt,  blight  (Pseudomonas  solanacearum  (EFS.) ). 
—  This  disease  of  the  tomato  is  widespread,  especially  in  the 
South,  and  prohibits  tomato  culture  upon  many  thousands  of 
acres  of  land.  It  occurs  especially  in  the  states  south  of 
Maryland,  and  has  also  been  noted  in  New  Jersey,  Delaware, 
Ohio,  and  Colorado. 

The  leaves  wilt,  either  singly  or  throughout  the  entire 
plant  at  once;  growth  stops  and  the  plant  dies.  The  stem 
appears  at  first  dirty  green,  then  brown,  then  black.  It  soon 
shrivels,  and  the  veins  become  brown  and  show  as  narrow 
black  lines,  or  in  section  as  black  dots.  The  wilting  of  the 
foliage  and  the  blackening  of  the  vascular  bundles  are  dis- 
tinctively characteristic. 

Soil  bearing  diseased  plants  one  season  remains  infested 
during  succeeding  years  and  must  be  abandoned  for  tomato 
culture.  The  disease  is  spread  from  plant  to  plant  largely 
by  the  potato  bug  (Colorado  beetle)  and  other  insects. 
For  this  reason  all  leaf-infecting  insects  should  be  given 
special  attention.  In  other  respects  this  disease  in  symp- 
toms, cause,  dissemination,  and  treatment  is  similar  to 
the  usual  soil  diseases. 

Another  wilt,  similar  but  of  slower  development,  is  de- 
scribed as  caused  by  Bacterium  michiganense  EFS.^"*' 

Wilt  ^^^  {Fusarium  lycopersici  Sacc.  and  Fusarium  sps). — 
This  wilt  is  also  widespread.     It  occurs  not  infrequently 


Vegetable  and  Field  Crops 


261 


as  the  cause  of  partial  or  even  total  losses  of  the  crop. 
The  plants  usually  reach  considerable  size,  blossom,  and 
set  fruit  before  showing  the  disease,  which  first  appears 
in  the  field  on  single  plants,  generally  sickly  looking,  and  of 
unhealthy  color,  followed  by  symptoms  of  wilt.  In  the 
worst  cases  all  of  the  plants  die  before  the  end  of  the  growing 
season,  sometimes  quite  suddenly  at  the  last;  or  the  crop 
may  mature  with  plants  missing  more  or  less  extensively.  If 
a  l)a(lly  affected  or  dead  plant  l)e  pulled  up,  the  roots  are 


I  i« ..  1  12.    -  Tuiuatu  licld  showjag  effect  of  wilt. 

found  to  be  decayed.  If  a  plant  is  pulled  up  as  soon  as  it 
begins  to  show  wilting,  the  roots  look  healthy  and  sound, 
but  close  inspection  shows  that  many  of  the  larger  laterals  are 
decayed  at  the  ends.  The  disease  consists  of  a  dry  rot  of  the 
roots,  commencing  at  the  ends  and  working  upward. 

The  first  symptom  is  a  pale  yellowish  color  of  the  lower 
leaves,  which  soon  dry  from  the  tip  toward  the  base  without 
spotting.  The  veins  and  woody  portion  of  the  stem  are 
darkened,  especially  upon  the  side  bearing  the  diseased 
leaves. 

As  to  means  of  dissemination  and  control,  what  is  said 
under  soil  diseases  will  apply. 


262 


Diseases  of  Economic  Plants 


Leaf -mold  (Cladosporium  fulvum  Cke.),  —  Under  glass 
in  the  North  and  occasionally  in  the  open,  especially  in  the 
South,  this  disease  is  destructive.  It  occurs  as  rusty  or 
cinnamon  brown  blotches  on  the  lower  side  of  the  leaf,  which 

turns  yellow  above,  then 
brown  or  black,  curls,  and 
dies.  The  loss  of  food 
supply  consumed  by  the 
parasite,  together  with  the 
loss  through  destruction 
of  the  leaf  green,  injures 
the  yield  seriously. 

Indoors  ventilation  is 
the  best  remedy,  coupled 
with  clean  culture  to  avoid 
carrying  the  pest  over  to 
another  year.  On  fields 
Bordeaux  mixture  would 
doubtless  serve  well. 

The  causal  fungus  of 
this  disease  was  first  de- 
scribed in  1883  by  Cooke 
from  specimens  collected 
in  North  Carolina. 

Leaf-spot  ^^^  (Septoria 
ly  coper  si  ci  Speg.).  —  A 
very  common  leaf -spot 
has  almost  precisely  the 
general  appearance  illus- 
trated in  Fig.  143,  except 
that  small  pycnidia  occupy  the  spots.  It  is  known  through- 
out the  United  States,  South  America,  Europe,  and  Australia, 
and  often  causes  large  loss.  In  some  states  it  is  the  most 
important  tomato  disease.  The  total  loss  in  the  United 
States  is  estimated  as  $5,000,000  annually. 

The  disease  attacks  the  older  loaves  first  and  proceeds 
toward  the  top  of  the  plant,  often  causing  the  loss  of  so 


Fig.    143.  —  Tomato    leaf 
spots  of  mold. 


showing 


Vegetable  and  Field  Crops  263 

many  leaves  as  to  give  the  plant  the  appearance  of  blight, 
and  resulting  in  complete  ruin  of  the  crop.  The  presence 
of  the  leaf-spot  distinguishes  this  from  any  of  the  blights. 
Spraying  with  Bordeaux  mixture  is  effective  against  this 
disease  though  valueless  against  the  various  wilts.  Especial 
attention  should  be  given  to  guard,  by  spraying,  the  seedlings 
in  the  seed  bed,  using  a  weak  Bordeaux  mixture.  Moving 
among  the  plants  when  they  are  wet  spreads  infection.  All 
refuse  should  be  burned  or  plowed  under. 

Downy-mildew,  late-blight  ^'^  {Phijtophthora  infestans 
(Mont.)  De  Bary).  —  Arising  from  the  same  cause  as  the 
dreaded  potato  blight,  of  which  host  the  tomato  is  close  kin, 
is  the  tomato  blight  which  causes  large  loss  of  the  crop  in 
some  sections  of  California.  It  has  been  reported  also  in 
Massachusetts  and  Colorado. 

As  with  the  potato,  the  amount  of  damage  is  closely 
dependent  upon  weather  conditions,  the  disease  being  greatly 
favored  by  a  warm,  humid  atmosphere.  It  appears  suddenly 
as  dark,  discolored  spots  on  the  fruit  and  other  green  parts. 
On  the  fruit  the  spot,  usually  upon  the  upper  side,  is  watery 
and  large.  Many  tomatoes,  apparently  healthy  when 
picked,  rot  in  shipment,  the  rot  being  accompanied,  under 
humid  conditions,  by  a  fine,  white  surface  mold.  Dark  spots 
upon  stems  and  branches  soon  extend  throughout  the  whole 
plant,  giving  it  the  appearance  of  one  stricken  by  frost. 

Protective  spraying  with  5-5-50  Bordeaux  mixture,  as 
recommended  for  the  potato,  will  probably  serve  in  case  of 
this  disease.  In  regions  of  infrequent  rainfall  it  is  neces- 
sary to  spray  only  after  each  rain. 

Fruit-rot  ^^''  {Phoma  destrudiva  Plow.).  —  Leaf-spots  are 
present,  but  it  is  as  a  spot  upon  either  green  or  ripe  fruit  that 
greatest  injury  is  incurred.  The  spots  are  1-3  cm.  in  diam- 
eter, brownish-black,  and  depressed.  This  trouble  is  most 
prevalent  on  tomatoes,  originating  in  the  South,  and  shipped 
to  northern  markets,  and  on  such  fruits  causes  heavy  losses. 

Blossom-end  rot.  —  Readily  recognized  from  its  name, 
this  troublesome  disease  is  essentially  a  dry,  black  rot  ap- 


264  Diseases  of  Economic  Plants 

pearing  on  the  blossom  end  and  injurious  chiefly  to  early 
tomatoes.  It  is  especially  harmful,  owing  to  the  high  value 
of  the  early  fruit  that  it  destroys.  Various  factors  have  been 
named  as  the  cause,  and  it  cannot  yet  be  said  with  certainty 
which  is  responsible. 

The  trouble  is  more  serious  upon  droughty  soils  and  can 
to  some  extent  be  controlled  by  irrigation  or  moisture  con- 
servation, i.  e.,  increasing  the  water-holding  power  of  the 
soils  by  the  addition  of  organic  matter  and  surface  tillage. 

Early-blight  {Allernaria  solani  (E.  &  M.)  J.  &  G.). — 
Ruin  is  brought  to  the  crop  in  many  seasons,  particularly 
in  the  southernmost  states,  by  this  blight,  which  is  identical 
with  the  potato  early-blight.  The  leaves  bear  numerous, 
small,  usually  angular  spots,  often  concentrically  marked, 
which  appear  first  as  minute  brown  specks,  later  showing  a 
pale  center  with  a  darker  border.  In  badly  affected  leaves  the 
tips  dry  and  curl  up.    Petioles  and  stems  are  also  attacked. 

Thorough  spraying  with  the  usual  Bordeaux  mixture  should 
be  begun  at  the  first  indication  of  the  disease  and  continued 
weekly,  or  semiweekly  if  growth  is  rapid  and  the  weather 
damp.    Often  it  is  still  better  to  begin  spraying  in  the  seed  bed. 

Southern-blight  (Sclerotium  rolfsii  Sacc).  —  This  blight 
IS  often  completely  destructive  to  the  tomato  in  the  south- 
ernmost states.  The  first  sign  is  wilting  of  the  terminal  por- 
tion of  the  plant,  distinguishing  Southern-blight  from  other 
wilts,  which  commence  with  the  lower  leaves. 

For  discussion  and  treatment,  see  pepper. 

Leak  {Rhizopus  nigricans).  —  The  effect  is  much  as  on 
strawberries  and  the  loss  during  shipment  is  large. 

Minor  diseases 

Anthracnose  {Colletotrichiim  phomoides  (Sacc.)  Chest.).  — 
This  is  chiefly  a  disease  of  the  ripe  fruit,  cither  upon  the  vines 
or  after  harvest.  It  appears  as  sunken,  discolored  spots  with 
wrinkled  surfaces  and  black  specks,  the  acervuli.  The  disease 
does  much  damage  to  fruit  before  it  is  picked,  and  also  in- 
jures the  keeping  quality. 


Vegetable  and  Field  Crops 


265 


Sooty-mold  (Fumago  vagans  Pers.).  —  Dense,  olive-black 
growths  of  mold  form  upon  the  leaves.  Damping-ofif  occurs 
in  the  seed  bed.  Timber-rot  {Sderotinia) ,  see  lettuce. 
Buckeye-rot  {Phytophfhora  terrestria)  is  a  zonate,  hard  rot  of 
fruit.  Winter-blight.  —  Loss  of  $2,500  in  one  house  is  re- 
ported, but  the  disease  is  not  generally  distributed.  Develop- 
ment is  dwarfed,  and  the  stems  show  brown  lesions  in  cortex 
and  bundles,  but  no  parasite  has  been  demonstrated.  Ro- 
sette ^^^  {Corticinm,  vagum).  —  This  is  identical  with  the 
potato  black-scurf,  showing 
similar  lesions  upon  the  root 
and  stem  near  the  ground. 
The  tops  have  long  inter- 
nodes  and  dwarfed  leaves 
which  are  somewhat  curled. 

Upon  the  ripe  fruits,  espe- 
cially those  touching  the 
ground,  this  disease  occurs 
as  a  brown  rot  upon  a 
slightly  wrinkled  epidermis. 
Hollow-stem  appears  to  be 
due  to  miproper  growth  con- 
ditions. Blossom-drop  is  due  to  unknown  cause.  Leaf -roll  is 
similar  to  that  of  potato.    Root-knot  (nematodes)  is  common. 

(Edema.^^''  —  This  is  a  condition  of  overgrowth  of  certain 
cells  of  the  plant,  causing  swelling  of  veins  and  leaf  tissues, 
and  curling  of  the  leaves  in  irregular  growth.  Usually 
confined  to  the  greenhouse,  it  is  caused  by  excess  of  water, 
lack  of  light,  improper  temperature,  and  especially  by  over- 
heated soil,  and  is  readily  controlled  by  careful  management. 

Chlorosis.  —  The  leaves  show  completely  whitened  areas. 
The  cause  is  unknown.  Mosaic.  —  Upon  the  tomato  appears 
a  mosaic,  similar  to  that  of  tobacco.  Aside  from  this  ap- 
parent kinship  little  is  known  about  it. 

TURNIP.    See  p.  165. 

WATERMELON.    See  p.  178. 


i^^sat^ 


Fig.  144.- 


—  Tomato  anthracnose. 
After  Heald. 


CEREALS 

Cereal  Smuts  in  General  ^-^ 

Dark  or  black  masses  usually  dusty,  though  sometimes 
compact,  replace  floral  parts,  grain,  glumes  (chaff),  or  in 
some  cases  involve  the  leaves  and  stem.  The  smut  mass  con- 
sists almost  wholly  of  the  spores  of  the  causal  fungus  which 
gains  entrance  to  the  plants  when  they  are  in  a  susceptible 
condition  of  development,  the  time  varying  with  different 
kinds  of  plants,  and  grows  within  the  plant  as  an  active 
parasite,  drawing  its  nourishment  from  its  involuntary  host. 
When  the  host  plant  has  attained  the  right  age,  and  corre- 
spondingly, too,  the  fungus  has  reached  its  proper  stage  of 
maturity,  the  disease  becomes  apparent  to  the  eye  as  the 
familiar  smut. 

Smut  spores  under  suitable  conditions  of  moisture,  food, 
and  heat  sprout,  and  produce  smaller  spores,  sporidia, 
which,  if  they  fall  upon  the  right  host  plant  in  the  proper 
period  of  its  development,  penetrate  into  it  and  grow. 
The  host  plant  may  or  may  not  outgrow  its  enemy.  In 
any  event,  its  presence  is  not  apparent  to  the  naked  eye 
until  the  period  of  maturity  arrives  again,  and  another  crop 
of  dark-colored  spores  is  produced. 

Kinds  of  smut.^-*^  —  In  all,  something  more  than  600 
species  are  now  recorded.  Over  205  of  these  are  founfl  in  the 
United  States,  growing  upon  some  442  different  kinds  of 
plants,  most  of  which  are  unimportant  and  wild;  although 
some  of  them,  such  as  the  corn  smut,  07iion  smut,  and  the 
smuts  of  wheat,  oats,  rye,  barley  attack  plants  of  high  eco- 
nomic value  and  cause  great  damage.  The  yearly  toll 
from  three  of  these  that  are  easily  preventable  has  been 
estimated  to  be  as  high  as  25,500,000  bushels  of  wheat, 
110,000,000  bushels  of  oats,  6,000,000  bushels  of  barley. 
266 


Cereals  267 

Negligence  thus  involves  a  total  of  more  than  100,000,000 
bushels  of  grain  annually. 

The  common  corn  smut  develops  upon  any  part  of  the 
corn  plant,  but  is  usually  most  conspicuous  upon  the  ear  and 
tassel.  Another  smut  of  corn  growing  only  upon  the  tassel 
is  less  widely  known.  Rye  smut  develops  mainly  in  the 
stem;  the  smut  of  oats,  wheat,  and  barley  in  the  ovary, 
the  grain;  onion  smut  grows  upon  the  leaves,  often  in 
the  bulb. 

It  is  evident  that  to  know  precisely  what  parts  and  at 
what  periods  the  various  crop  plants  are  open  to  infection 
is  of  utmost  importance  in  looking  to  the  prevention  of  the 
smuts.  It  was  early  proved  that  oats  are  susceptible  to 
infection  only  in  the  early  stages  of  their  development. 
The  exact  work  of  Brefeld  proved  that  corn  is  susceptible  to 
infection  on  all  young,  tender,  growing  parts,  and  in  1896 
Maddox,  Brefeld,  antl  others  showed  that  in  the  case  of  the 
loose  smut  of  wheat  and  the  barley  smut  infection  occurs 
while  the  plant  is  in  bloom,  this  infection  affecting  the  seeds 
and  resulting  in  smutted  plants  in  the  crop  raised  from  such 
infected  seeds. 

It  is  upon  these  facts  that  our  present  modes  of  preven- 
tion are  based.  The  treatment  for  oat  smut  is  such  as  to 
kill  the  spores  adhering  to  the  grain  and  thus  prevent  in- 
fection during  the  period  of  susceptibility,  i.  e.,  the  very 
young  seedling  condition.  The  same  treatment  is  effec- 
tive for  the  stinking  smut  of  wheat.  The  loose  smut  of 
wheat  gaining  entrance  to  the  plant  before  the  grain  is 
harvested  cannot  be  prevented  by  such  means  without 
danger  to  the  seed,  but  can  be  prevented  by  the  use  of  clean, 
uninfected  seed.  Corn,  being  susceptible  at  all  ages  of  its 
growth,  cannot  be  protected  by  seed  treatment. 

Owing  to  their  great  damage  and  conspicuousness,  smuts 
have  attracted  attention  from  very  early  times,  and  man}^ 
references  to  them  are  found  in  ancient  writings.  Probably 
not  until  1791,  however,  was  their  true  nature  as  vegetable 
parasites   recognized.      Man}^   were    the   means   that   were 


268 


Diseases  of  Economic  Plants 


suggested  for  the  prevention  of  these  pests:  placing  laurel 
branches  in  the  field,  change  of  seed,  avoidance  of  manures, 
thorough  screening,  soaking  in  brine,  etc. 


Fig.  145.  —  Oat  plants,  smutted  and  healthy;  note 
difference  in  height. 

Preventive  treatments,  —  One  early  remedy  that  has 
proved  its  value  and  remained  in  common  use,  soaking  the 
seed  in  copper  sulfate,  was  first  tried  l)>'  Tessier  in  1789,  after 
he,  in  1786,  and  Young,  in  1787,  had  tested  numerous  chem- 


Cereals  269 

icals.  His  test  was  without  results,  since,  during  the  season 
of  his  experiment,  neither  treated  nor  untreated  wheat  was 
smutted.  Prevost  of  France  in  1807  was  the  first  to  publish 
an  account  of  the  successful  use  of  copper  sulfate  for  wheat 
smut.  He  recommended  a  solution  of  about  6  per  cent 
strength,  and  the  remedy  was,  and  is,  still  widely  used.  Solu- 
tions vavying  in  strength  have  been  employed,  one-half  per 
cent  being  most  highly  recommended.  In  1873  Dreisch 
improved  the  copper-sulfate  treatment  by  using  limewater 
following  the  copper  sulfate;  thus,  to  a  large  extent,  diminish- 
ing the  amount  of  seed  killed  by  the  treatment. 

Jensen,  a  Dane,  in  1887  and  1888  reported  excellent 
results  with  oat,  barley,  and  wheat  smuts  from  dipping 
the  seed  in  hot  water.  Untreated  seed  gave  36  per  cent  of 
smut.  One-fourth  per  cent  of  copper  sulfate  gave  one-half 
per  Cent  smut.  Warm  water,  56°  C.  (133°  F.)  for  five  minutes, 
gave  no  smut.  Kellerman  and  Swingle  soon  afterward  in- 
troduced this  last  treatment  into  this  country. 

In  1888  the  germicidal  action  of  formalin  was  discovered 
and  this  substance  was  used  as  a  preventive  for  oat 
smut  by  Bolley  of  North  Dakota  during  the  years  1894 
to  1897.=*-^ 

The  use  of  the  various  smut  remedies  is  usually  attended 
by  an  increase  in  vigor  of  the  plants,  and  by  an  increase 
in  yield  in  excess  of  that  due  simply  to  the  elimination  of 
the  smutted  grains.  Thus  increases  of  over  4  bushels  per 
acre  have  been  found  in  wheat  fields  in  which  only  about 
\}/2  bushels  were  destroyed  by  smut.  Similarly,  with  oats, 
the  increase  in  jdeld  is  often  five  times  as  great  as  the  quan- 
tity of  grain  lost  by  smut  in  fields  not  treated.  This  may 
be  due  to  elimination  of  the  fungus  from  plants  which  other- 
wise would  have  to  resist  it  throughout  a  portion  of  their 
growth  period  or  it  may  be  due  to  the  killing  of  spores  of 
numerous  fungi  other  than  those  of  smut  on  the  seed  which 
exert  an  adverse  influence  during  and  following  germination. 
An  excellent  account  of  the  early  history  of  smuts  in  general 
may  be  found  in  the  Report  of  the  Kansas  Agricultural 


270  Diseases  of  Economic  Plants 

Experiment  Station  for  1889,  and  a  comprehensive  article 
upon  corn  smut  in  the  Twelfth  Report  of  the  Indiana  Agricul- 
tural Experiment  Station. 

Present  methods  of  seed  treatment.^-^-  ^-^  —  Preliminary 
to  any  form  of  seed  treatment,  the  seed  should  be  thoroughly 
cleaned ,  in  some  cases  floating-out  of  the  spore-filled  grains  is 
necessary,  and  after  treatment  it  should  be  protected  from 
contamination.  Sacks,  bins,  drills,  etc.,  with  which  seed  will 
come  in  contact,  should  be  disinfected  with  formalin. 

The  common  methods  of  cereal  seed  treatment  now  are  by 
formalin,  hot  water,  or  copper  sulfate.  The  first  is  simpler  and 
easier  and  is  preferable  whenever  it  is  effective.  In  treating 
for  certain  kinds  of  smut,  however,  the  formalin  treatment  is 
not  so  effective  as  is  the  hot-water  method.  These  three 
methods  with  their  limitations  are  as  follows: 

The  formalin  wet  method.  —  The  seed  to  be  treated  is 
either  dipped  in  the  solution  of  formalin,  1  pint  to  30  or 
40  gallons  of  water,  or  this  solution  is  sprinkled  on  the  seed, 
with  thorough  mixing,  at  the  rate  of  one  gallon  to  each 
bushel  of  seed.  The  pile  is  then  blanketed  and  later  spread 
out  to  dry. 

In  a  modification  known  as  the  formalin  dry  method  ^-^  the 
seed  is  shoveled  from  one  pile  to  another  and  each  shovelful  is 
sprayed  or  sprinkled  with  a  solution  consisting  of,  formalin 
(37  per  cent  formaldehyde)  diluted  with  an  equal  amount 
of  water,  and  applied  at  the  rate  of  one  quart  (1  pint  of 
formalin)  to  50  bushels  of  seed.  A  quart  sprayer  is  conven- 
ient for  use.  After  treating,  the  seed  should  be  blanketed 
for  five  hours,  when  it  is  ready  for  planting.  Workmen 
will  find  the  formalin  irritating  to  the  mucous  membrane, 
and  therefore  should  apply  the  solution  as  directly  as  possi- 
ble to  the  seed.  A  variation  from  this  method  is  to  mix  1 
pint  of  formalin  with  10  or  12  gallons  of  water  and  sprinkle 
on  the  seeds  as  they  are  shoveled  over.  They  may  then  be 
sacked  immediately  and  sowed  next  day.  This  method, 
employing  a  strong  solution,  seems  to  be  both  safe  and 
efficient  with  oats,  but  its  use  with  wheat  and  other  grains  is 


Cereals  271 

still  in  the  experimental  stage  and  is  apparently  attended  with 
danger  to  the  seed. 

On  a  large  scale,  oats  may  be  treated  by  the  formalin 
method  at  the  rate  of  500  bushels  an  hour,  by  throwing  the 
formalin  solution,  by  means  of  a  steam  pump,  against  the 
grain  as  it  falls  through  elevators  arranged  with  deflectors  so 
as  to  give  proper  contact.^" 

The  formalin  treatments  as  above  given  are  effective 
against  those  smuts  in  which  the  spores  lie  upon  the  surface 
of  the  seeds  and  in  which  the  smut  fungus  is  not  within  the 
seed  itself,  e.  g.,  oat  smuts,  wheat  bunt,  covered  smut  of 
barley  and  rye,  rice  smut,  sorghum,  and  millet  kernel-smut. 

Long  time  formalin  treatment.  —  Seeds  are  immersed  for 
two  hours  in  the  formalin  solution,  1  pint  to  40  gallons  of 
water.  Favorable  results  are  reported  even  in  those  cases  of 
floral  infection  where  the  hot-water  treatment  was  formerly 
thought  necessary,  e.  g.,  in  the  cases  of  wheat  loose  smut  and 
the  covered  smut  of  barley,  but  complete  reliability  of  this 
treatment  for  these  diseases  is  not  yet  demonstrated. 

Copper-sulfate  treatment.  —  This  is  the  oldest  effective 
treatment  of  cereal  seeds.  It  has,  however,  on  account  of  its 
greater  cost  and  the  larger  injury  done  to  the  seed,  in  the 
main  been  superseded  by  formalin  methods.  It  is  effective 
against  the  same  smuts  for  which  formalin  is  used,  but  is 
recommended  only  where  there  is  heavy  soil  infestation.  A 
solution  of  1  pound  of  copper  sulfate  and  1  pound  of  common 
salt  to  5  or  10  gallons  of  water  is  used,  and  the  seed  either 
soaked,  sprinkled,  or  dipped.  Treatment  should  be  com- 
pleted by  dipping  or  sprinkling  with  milk  of  lime  (1  pound  of 
quicklime  to  10  gallons  of  water). 

The  hot-water  treatment  ^-^  is  employed  for  those  smuts  in 
which  the  fungus  is  within  the  seed,  not  superficial.  There 
are  three  forms:  1,  the  short  treatment;  2,  the  modified  hot- 
water  treatment;  3,  the  long  treatment  or  pasteurization. 
The  first  consists,  in  general,  in  subjecting  the  seed  to  water 
at  a  temperature  ranging  from  52°  C.  (120°  F.)  to  61°  C. 
(142°  F.)  for  10  to  15  minutes.      It  is  of  use  in  only  those 


272  Diseases  of  Economic  Plants 

cases  where  formalin  can  be  used,  and  will  therefore  not  be 
described  further.  The  directions  for  the  modified  hot-water 
treatment,  drawn  from  Freeman  and  Johnson, ^-'^  with  slight 
changes,  are  as  follows: 

After  the  seed  has  been  cleaned  by  thorough  fanning  and 
sifting,  it  should  l)e  soaked  for  from  five  to  seven  hours 
in  water  at  ordinary  room  temperature,  17°  to  22°  C.  (63° 
to  72°  F.),  then  placed  in  small,  loose  sacks  or  wire  baskets, 
containing  not  more  than  one-half  peck  each,  and  drained 
for  a  short  time.  The  seed  must  be  treated  in  small  lots 
in  order  that  all  of  the  grain  may  quickly  and  uniformly 
reach  the  desired  temperature.  Two  tubs  or  vats  of  water 
should  be  provided.  In  one  tub  (No.  2)  the  exact  tempera- 
ture required  should  be  maintained.  The  other  tub  (No.  1) 
is  used  for  bringing  the  grain  to  the  temperature  of  the 
treatment,  so  as  not  to  lower  the  temperature  in  tub  No.  2. 
Galvanized  iron  tubs  of  20  to  40  gallons  capacity,  and 
kerosene  or  gasoline  double-burner  stoves,  are  convenient. 
The  drained  sacks  or  baskets  of  seed  should  be  plunged  into 
tub  No.  1  for  a  minute,  then  transferred  to  tub  No.  2,  and 
kept  agitated  while  immersed  at  temperatures  and  for  the 
periods  specified  below,  the  temperatures  mentioned  being 
maintained  as  nearly  as  possible:  For  barley,  13  minutes 
at  52°  C.  (125.6°  F.);  for  wheat,  10  minutes  at  54°  C. 
(129.2°  F.).  In  treating  barley,  if  the  temperature  should 
rise  above  52°  C.  (125.6°  F.),  the  time  of  immersion  must 
be  reduced  to  ten  minutes  at  53°  C.  (127.4°  F.),  or  five  min- 
utes at  54°  C.  (129.2°  F.).  Above  54°  C.  (129.2°  F.)  there 
is  no  safe  margin.  If  the  temperature  falls  slightly  below 
52°  C.  (125.6°  F.),  the  time  of  treatment  should  be  increased 
in  proportion.  A  temperature  lower  than  51°  C.  (123.8°  F.) 
is  not  effective.  In  treating  wheat,  if  the  temperature  should 
rise  above  54°  C.  (129.2°  F.)  or  fall  lielow  52°  C.  (125.6°  F.), 
the  time  for  immersion  must  be  diminished  or  increased  ac- 
cordingly. Under  no  circumstances  should  a  temperature  of 
more  than  55°  C.  (131°  F.)  be  allowed.  Temperatures  be- 
low 51°  C.  (123.8°  F.)  are  ineffective.    A  reliable  thermometer 


Cere  ah 


273 


is  necessary,  since  the  use  of  an  inaccurate  instrument  may 
result  in  injury  to  the  germinating  power  of  the  grain  or  in 
failure  to  prevent  the  smut.  At  the  end  of  the  period  of 
treatment,  the  grain  should  be  transferred  to  a  cold  bath  to 
terminate  the  action  of  the  heat. 

Two  men  working  together  can  easily  treat  one  bushel 
of  grain  an  hour,  or  enough  seed  in  one  day  to  sow  a  seed 


(      JBoiling  water. 


Post. 


Fig.  146.  —  Diagram  showing  a  convenient  arrangement  of  utensils  for 
the  Jensen  hot-water  treatment.    After  Swingle. 


plat  of  from  6  to  10  acres.  The  seed  may  be  dried  by  spread- 
ing it  out  in  thin  layers,  not  over  5  cm.  in  depth,  on  a  clean 
granary  floor  or  on  canvas,  and  shoveling  or  raking  it  from 
time  to  time.  It  should  not  be  allowed  to  sprout.  Care  must 
be  taken  to  prevent  freezing  of  the  grain  when  it  is  moist, 
as  this  will  impair  germination. 


274  Diseases  of  Economic  Plants 

Seed  treated  as  indicated  may  be  planted  as  soon  as  it  is 
sufficiently  dry  to  run  freely  through  the  drills,  making  al- 
lowance for  the  swollen  seed. 

The  long  hot-water  treatment  or  pasteurization  consists  in 
subjecting  the  seed  to  a  temperature  of  45°  C.  (113°  F.)  for 
three  hours,  the  permissible  range  being  44°  to  46°  C.  (1 1 1°  to 
115°  F.).  The  advantages  of  this  method  are  greater  effi- 
ciency, less  danger  of  killing  the  seed,  and  the  need  of  but  a 
single  bath.  It  is  difficult,  however,  to  maintain  the  proper 
temperature  for  so  long  a  time. 

These  hot-water  treatments,  though  effective  against  both 
smuts  of  wheat  and  of  barley,  are  used  primarily  for  the  loose 
smuts  of  barley  and  wheat,  and  are  generally  combined  with 
the  seed-plat,  see  p.  275,  and  rogueing.  Hot-water  treat- 
ments are  much  simpler  and  more  accurate  of  application 
if  steam  is  available  for  heating  purposes. 

Injury  to  seed  by  treatment.  —  The  germinating  power  of 
treated  seed  should  be  tested,  and  if  low,  the  rate  of  planting 
should  be  correspondingly  increased.  The  formalin  treat- 
ment does  but  inappreciable  injury  to  sound  seed,  though 
cracked  seed  are  injured  by  chemicals.  The  softer  wheats  are 
more  often  cracked  than  the  harder  varieties,  therefore  are 
more  liable  to  injury  by  chemical  treatments.  Seed  sub- 
jected to  wetting  may  be  injured  in  germination  power  if 
dried  too  slowly.  However,  poor  stands  attributed  to  seed 
injury  often  are  really  due  to  the  use  of  too  little  seed,  since 
the  treated,  swollen  grain  feeds  more  slowly  through  the  drill. 
The  sensitiveness  of  various  seeds  ^-''  to  treatments  is 
indicated  in  the  following  table.  0  shows  no  injury,  tr  a  trace 
only,  H — 1-+  very  serious,  4-+  less  serious.  It  is  to  be  added, 
however,  that  some  experimenters  report  injury  to  wheat  from 
the  dry  treatment. 

Wheat  Rye  Oats  Barley 

Formalin 

Dip 0  0  0  0 

Sprinkle 0  0  0  0 

Dry 0  0  0  0 

Soaking  1  hour 0  0  0 


Cereals  275 

Wheat  Rye                 Oats             Barley 
Copper  sulfate 

10  minutes 0  0                 +  +  +               tr 

Long  time +  +  +  +  +  + 

Hot  water 

133°  12  minutes +  +  +  +  +  +  0  tr 

101-115°  3  hours tr  tr 

Modifietl 

129°  10  minutes ++  tr 

The  Seed  Plat.  — A  good,  clean,  well-cultivated  piece  of 
land  should  be  selected  for  raising  seed.  The  plat  should  be 
large  enough  to  provide  at  least  twice  as  much  grain  as  will  be 
necessary  for  farm  seed  the  following  year  in  order  to  allow 
for  loss  in  cleaning  and  selecting.  This  seed  plat  should  not  lie 
near  fields  of  smutted  crops  of  the  same  cereals,  nor  should 
it  be  so  located  that  the  prevailing  winds  at  flowering  time 
can  carry  spores  to  the  seed  plat  from  a  neighboring  field 
of  the  same  grain.  This  isolation  is  absolutely  necessary. 
A  strip  of  wood,  a  cornfield,  or  a  large  meadow  is  a  valuable 
protection.  In  this  plat  should  be  planted  seed  treated  by 
the  hot-water  methods.  The  seed  plat  may  be  maintained 
from  year  to  year,  as  long  as  any  smut  is  present  in  the  grain 
fields. 


Cereal  Rusts  in  General 


328 


The  rusts  constitute  a  complex,  intricate,  difficult,  but 
interesting  group  of  diseases.  It  is  said  that  the  "average 
annual  loss  from  rust  throughout  the  United  States  far 
exceeds  that  due  to  any  other  enemy,  insect  or  fungous, 
and  often  equals  those  from  all  others  combined." 

The  black-stem-rust  alone  in  the  United  States  and 
Canada  in  1916  was  estimated  to  have  caused  a  loss  of  about 
280,000,000  bushels  of  wheat  and  additional  loss  on  oats, 
barley,  and  rye. 

The  rusts  in  their  most  complete  form  exhibit  three  dis- 
tinct stages  (cf.  p.  150).  The  spring  stage,  or  cluster-cup, 
consists  of  a  group  or  cluster  of  very  minute,  cup-like,  spore- 


276  Diseases  of  Economic  Plants 

bearing  regions.  These  cups  are  sunken  in  the  tissue  of  the 
host,  often  with  their  rims  only  protruding.  The  second,  or 
summer,  stage,  also  called  the  uredinial  stage,  is  of  entirely 
different  appearance,  consisting  usually  of  elongated  sori, 
bearing  a  mass  of  spores  the  color  of  iron  rust  or  verging 
toward  orange  or  yellow.  These  spore  masses  are  at  first 
covered  by  the  epidermis  of  the  host,  but  this  covering 
eventually  ruptures,  disclosing  the  usually  dusty  or  pul- 
verulent mass  of  spores,  surrounded  by  a  fringe  of  the  re- 
maining epidermis.  The  third,  winter  or  telial,  stage  consists 
of  sori  almost  exactly  like  those  of  the  uredinial  stage  except 
that  the  spores  within  are  usually  darker  in  color  and  in 
a  compact,  cushion-like  mass.  The  sorus  is  often  identical 
in  the  two  latter  stages,  a  uredinium  gradually  changing  as 
the  season  advances  into  a  teliuni. 

These  three  stages  have,  in  general,  three  separate  func- 
tions. The  function  of  the  teliospores  is  to  live  over  winter 
or  over  the  long  resting  period  of  the  fungus.  They  are 
essentially  long-lived  and  hardy.  The  cluster-cup  spores 
multiply  and  spread  infection,  especially  in  the  earliest  part 
of  the  season.  The  urediniospores  continue  the  multiplica- 
tion and  infection  throughout  the  growing  season  of  the  host. 
The  last  two  forms  of  spores  are  in  general  comparatively 
short-lived.  If  the  host  plant  remains  alive  over  winter,  as  is 
the  case  with  winter  wheat,  the  fungus,  in  the  South,  may 
continue  to  grow  and  produce  summer  spores  throughout 
the  winter.  Even  in  colder  climates  the  urediniospores 
of  some  rusts  live  over  winter  and  start  infection  in  the 
spring. 

In  the  case  of  some  rusts  these  three  forms  are  all  known 
to  be  present.  In  the  case  of  other  rusts  one  stage  or  even 
two  stages  may  either  be  unknown  or  may  not  exist  at  all. 
When  all  three  stages  do  exist,  the  spring  stage  often  develops 
upon  some  host  other  than  that  bearing  the  uredinial  and 
telial  stages.  Thus  the  spring  stage  of  the  wheat  rust  is 
found  upon  the  barberry;  of  corn  upon  oxalis;  of  oats  upon 
buckthorn. 


Cereals 


277 


That  some  intimate  relation  existed  between  the  bar- 
berry bush  and  the  black-stem-rust  of  wheat  was  suspected 
very  early  in  the  seventeenth  century,  and  in  1660  a  barberry 
eradication  law  was  passed  in  France,  while  between  1726  and 
1779,  Connecticut,  Rhode  Island,  and  Massachusetts  did  like- 
wise. In  1818  Schroeter,  a  Danish  school-teacher,  published 
many  observations  concerning;  the  relation  of  the  cluster-cup 
upon  the  barberry  and  the  rust  of  grains.  This  relation  was 
finally  definitely  proved  by  De  Bary  in  1865,  who,  by  sowing 
the  teliospores  from  the  wheat  upon  the  barberry,  produced 
the  cluster-cups. 

Some  rusts  are  closely  limited  in  host  range  and  can  grow 
on  very  few,  perhaps  on  only  one  host ;  others  are  able  to  grow 
on  various  hosts.  The  host  relation  of  several  important 
cereal  rusts  is  shown  in  the  following  table :  ■'^^ 


^ 

=) 

Also  on  other  genera  of  grasses 

o 

■2 

-T" 

■^ 

e 

s 

== 

O 

ttS 

oq 

b^ 

q; 

Puccinia 

0 

tr 

+ 

+ 

0 

+ 

Agropyron  0  sps.,  Elymus  3  sps., 

gramims 

Hordeum  4   sps.,   Hystrix   1   sp., 

secalis 

Secale  1  sp.,  Sporobolus  1  sp., 
Bromus  2  sps.,  Avena  sativa  and 
Triticum  vulgare. 

Puccinia 
graminis 

+ 

0 

tr 

+ 

0 

+ 

Agropyron  7  sps.,  Elymus  5  sps., 
Hordeum  5   sps.,   Hystrix   1   sp., 

tritici 

Secale  1  sp.,  Triticum  8  sps., 
Bromus  3  sps.,  Alopecurus  1  sp. 

Puccinia 

0 

+ 

tr 

tr 

tr 

+ 

Avena  2   sps.,   Agrostis  3   sps., 

graminis 

Anthoxanthum   1   sp.,   Dactylis   1 

avenw 

sp.,  Klaeeria  1  sp.,  Panicularia  1 
sp.,  Arrhenatherum  1  sp.,  Alope- 
curus 2  sps.,  Bromus 3  sps.,  Cala- 
magrostis  1  sp.,  Holcus  1  sp., 
Phalaris  1  sp.,  Agropyron  1  sp., 
Bcckmannia  1  sp.,  Elymus  2  sps., 
Festuca  2  sps.,  Hordeum  3  sps., 
Hystrix  1  sp.,  Lolium  3  sps., 
Phleum  1  sp.,  Secale  cereale. 

278 


Diseases  of  Economic  Plants 


1 

1 

1 

1 

05 

S 

1 

Puccinia 

0 

tr 

tr 

tr 

+ 

0 

graminis 
phleipra- 

tensis 

Puccinia 

0 

tr 

tr 

tr 

0 

+ 

graminis 

agrostis 

Puccinia 

graminis 

airce 

Puccinia 

graminis 

poa 

Puccinia 

+ 

0 

tr 

+ 

0 

+ 

graminis 

Iritici- 

compacti 

Puccinia 

+ 

simplex 

Puccinia 

+ 

tr 

+ 

0 

coronata 

Puccinia 

tr 

dispersa 

Puccinia 

tr 

purpurea 

Puccinia 

+ 

triticina 

Puccinia 

+ 

+ 

+ 

glumarum 

+ 

=host 

0 

=  llO  1 

nfect 

ion 

Also  on  other  genera  of  grasses 
as  beloiv 


Dactylis  1  sp.,  Festuca  2  sps., 
Kceleria  1  sp.,  Phleum  1  sp.,  Alo- 
pecurus  2  sps.,  Holcus  1  sp., 
Avena  2  sps. ,Arrhenatherum  1  sp., 
Bromus  1  sp.,  Elymus  1  sp.,  Hor- 
deum  2  sps.,  Lolium  2  sps.,  Secale 
cereale. 

Agrostis  3  sps.,  Alopecunis  2 
sps.,  Bromus  1  sp.,  Dactylis  1  sp., 
Holcus  1  sp.,  Kceleria  1  sp.,  Avena, 
1  sp.,  Calamagrostis  1  sp.,  Hor- 
deum  1  sp.,  Secale  1  sp. 

Aira  ccespitosa,  A.  hottnica. 


Poa  compressa,  P.  cccsia,  P.  pra- 
tensis. 


Agropyron  7  sps.,  Elymus  4  sps., 
Hordeum  2  sps.,  Triticum  7  sps., 
Bromus  1  sp.,  Secale  1  sp. 


Alopecunis  1  sp.,  Anthoxanthum 
1  sp.,  Avena  1  sp.,  Dactylis  1  sp., 
Elymus  1  sp.,  Hordeum  several 
species. 


Sorghum  vulgare,   and   i*?.   holo- 
penses. 


=rust  infects  weakly 


Cereals  279 

All  cereal  rusts  multiply  much  more  rapidly  in  damp 
than  in  dry  weather,  and  are  more  destructive  to  late  crops. 
There  is  no  evidence  that  these  maladies  can  be  carried  by 
seed  from  rusted  plants,  though  such  seeds  should  not  be 
used  for  seed  purposes,  since  they  do  not  have  stored  nourish- 
ment sufficient  to  give  the  seedling  a  vigorous  start. 

Great  difference  in  rust  resistance  has  been  shown;  thus 
while  one  variety  of  grain  was  so  badly  affected  as  to  yield 
only  23^  bushels  per  acre,  a  resistant  variety  under  the  same 
conditions  gave  383^  bushels. 

The  greatest  hope  lies  in  the  use  of  varieties  which  can 
resist  the  disease.  A  number  of  different  kinds  of  grain  are 
now  known  which  possess  sufficient  resistance  to  give  good 
yields  even  when  the  rust  is  in  its  worst  form.  Since  serious 
outbreaks  of  rust  must  be  looked  forward  to  with  certainty, 
the  item  of  rust  resistance  must  have  due  weight  in  the  selec- 
tion of  the  variety  to  be  grown. 

Several  varieties  of  oats  of  the  red  group,  among  them 
the  Burt,  Appier,  and  Cook  when  grown  in  the  Southern 
States,  are  known  to  possess  valuable  resistance  to  the  oat 
rust.  Similarly  there  is  large  difference  between  varieties  of 
wheat  as  to  rust  susceptibility. 

Early  maturity  in  oats  is  of  especial  value  in  that  it  enables 
the  plant  to  evade  the  heaviest  part  of  the  rust  attack.  Good 
drainage  and  clean  culture  conduce  to  plants  of  more 
resistance  to  rust,  as  does  also  good  preparation  of  the  seed 
bed.  Drilled  wheat  is  better  lighted  and  better  ventilated  and 
resists  rust  more  effectively  than  wheat  that  is  broadcast. 

Wild  grasses  that  harbor  rusts  identical  with  the  rusts 
of  crop  plants,  such  as  wild  meadow  oat  grass,  orchard 
grass,  wild  wheat  grasses,  quack  grass,  wild  rye  grasses, 
etc.,  may  propagate  the  fungus  and  increase  infection.  If 
such  grasses  are  rusted,  they  should  be  burned,  plowed 
under,  or  avoided  in  the  location  of  the  grain  fields. 

While  sprays  of  various  kinds  may  be  effective  in  checking 
the  spread  of  rusts,  the  use  of  such  means  of  prevention  is 
impracticable,  owing  to  the  nature  of  growth  of  the  crop, 


280  Diseases  of  Economic  Plants 

and  the  difficulty  and  expense  of  the  application.  Moreover 
the  question  of  use  of  such  treatment  is  complicated  by  the 
different  kinds  of  rusts  to  be  met  and  by  their  different 
behavior  in  different  seasons. 

Anthracnose  of  Cereals 

Anthracnose  ^"'^  {CoUetotrichum  cereale  Manns).  —  Upon 
many  cereals  and  forage  crops,  as  rye,  wheat,  oats,  orchard 
grass,  timothy,  red-top,  and  blue-grass,  occurs  a  blight, 
resulting  in  shriveling  of  the  grain  and  spotting  of  the  leaves 
and  stalks.  The  fungus  is  marked  by  small,  black  acervuli, 
located  upon  the  spikes,  stems,  and  sheaths.  The  chief  at- 
tack is  made  as  the  plants  approach  maturity. 

For  further  discussion,  see  rye. 

Special  Diseases  of  Cereals 
BARLEY. 

Loose-smut '^-^  {Ustilago  nuda  (Jens.)  K.  &  S.).  —  This 
disease,  previously  thought  insignificant,  seems  to  be  in- 
creasing in  importance.  It  now  often  causes  losses  in  Wis- 
consin and  Minnesota  of  from  5  to  10  per  cent  of  the  crop, 
and  is  generally  prevalent  in  this  country,  though  often 
unnoticed  on  account  of  the  early  season  of  its  development, 
and  its  absence  at  harvest  time.  Every  spikelet  of  the 
smutted  head  is  usually  affected  and  entirely  changed  into 
smut,  the  central  stalk  of  the  head  alone  escaping.  Adjacent 
leaves  are  also  occasionally  smutted. 

The  smut  masses,  when  they  first  appear,  are  covered  by  a 
white  or  gray  membrane  which  soon  ruptures,  loosing  a 
powdery,  olive-brown  mass  of  spores,  which  soon  blow 
away.  This  character  enables  one  to  distinguish  it  easily 
from  the  covered  smut.  Smutted  plants  head  early,  the 
smut  reaching  its  maximum  at  flowering  time,  though 
scattered  heads  of  smut  may  appear  at  other  periods.  The 
smutted  heads  stand  high  on  tall  stalks,  which  affords  ex- 
cellent wind  distribution  of  the  spores  to  the  surrounding 


Cereals 


281 


blossoms.  The  fungus,  reaching  the  blossoms,  gains  such 
foothold  upon  the  developing  grain  that  its  use  as  seed,  with- 
out treatment,  insures  a  smutted  seedling  as  offspring.     In 


Fig.  147.  —  Loose-smut  of  barley  in  various  stages  of  develo]iinent. 
After  Johnson. 

the  plant  developing  from  such  an  infected  seedling  the 
disease  does  not  show  externally  mitil  the  smut  ripens  at  the 
next  blossoming  season. 

The  life  history  of  this  smut  is  thus  similar  to  that  of 


282  Diseases  of  Economic  Plants 

wheat  loose-smut,  and  the  same  treatment,  i.  e.,  rogueing, 
combined  with  a  modified  Jensen  hot-water  treatment,  is 
effective.    See  p.  272. 

Covered-smut^-^  (Ustilago  hordei  (Pers.)  K.  &  S.). — 
In  the  covered-smut,  the  smut  masses  replacing  the  grains 
and  glumes  are  at  first  covered  by  a  membrane  composed  of 
the  outer  surface  of  the  glumes  of  the  spikelet.  This  mem- 
brane retains  the  spores  for  some  time  after  harvest.  The 
spores,  as  seen  en  masse,  after  the  rupture  of  this  cover  are 
very  dark  to  purplish  black,  with  no  tint  of  olive. 

The  formalin  treatment  applies  here. 

Ergot.    See  rye. 

Black-stem-rust  (Puccinia  graminis  Pers.). —  The  forms  oc- 
curring on  both  wheat  and  rye  develop  equally  well  on  barley, 
and  severe  attacks  of  either  form  are  common.     See  wheat. 

Dwarf -leaf-rust  {Puccinia  simplex  (Koern.)  E.  &  H.).  — 
Reported  from  Iowa  in  1896,  later  from  California,  Minne- 
sota, Virginia,  Wisconsin,  Wyoming,  and  Maryland,  this  rust 
seems  to  be  of  recent  introduction  and  generally  of  minor 
importance,  though  serious  in  the  extreme  West. 

Blight  ^^°  (Pseudomonas  translucens  J.  J.  &  R.).  —  Water- 
soaked  areas  appear  on  the  leaves  extending  in  longitudinal 
stripes  or  blotches  between  the  veins.  Later  they  turn  brown. 
Small,  gray  drops  of  exudate  appear  on  either  leaf  surface. 
Distortion  of  the  head  may  be  caused  by  disease  of  the  en- 
veloping leaf.  It  has  been  observed  in  nine  states  from 
Ohio  to  Oregon,  on  many  varieties  of  barley.  Infection  ap- 
pears to  be  by  means  of  the  seed. 

Stripe-disease  (Pleospora  graminewn  Diet.,  Helmintho- 
sporium) .  —  This  leaf  blight  was  discovered  in  America 
by  Pammel  in  1890.  It  is  characterized  by  longitudinal, 
yellowish-green  spots  in  parallel  rows  upon  the  leaves.  The 
plants  die  prematurely,  and  the  yield  is  thus  reduced.  It  is 
reported  from  many  states.  The  loss  in  some  fields  amounts 
to  from  10  to  50  per  cent  of  the  crop.  Stripe  is  almost  en- 
tirely prevented  by  formalin  seed  treatment  (1  pt.  to  30  gals., 
2  hrs.). 


Cereals  283 

Net-blotch  ^^^  {Helminthosporium  teres  Sacc).  —  First 
known  in  the  United  States  in  1907,  this  disease  has  been 
observed  in  Iowa,  South  Dakota,  Minnesota,  and  Sas- 
katchewan. It  occurs  as  brownish,  circular,  or  somewhat 
elongated  dark  spots  which  soon  cause  the  leaves  to  turn 
brown.  It  also  occurs  upon  sheaths,  glumes,  spikelets,  and 
grain.    The  straw  at  harvest  is  dull  brown  and  lacks  strength. 

Scab,  Powdery-mildew,  Yellow-stripe-rust.    See  wheat. 

BROOM    CORN 

Kernel-smut''''-  (Sphacelotheca  sorghi  (Link)  Clinton). — 
Irregular,  elongated  branches  of  inferior  value  indicate  the 
presence  of  the  smut.  The  branches  are  further  damaged  by 
blackening  occasioned  by  the  loose  spores.  The  seeds  are 
destroyed.  Of  the  fields  examined  by  Clinton  in  Illinois  few 
showed  over  1  per  cent  of  the  stalks  infected,  though  some- 
times parts  of  a  field  bore  as  high  as  20  per  cent  of  diseased 
stalks.  Infection  can  occur  only  upon  very  young  plants. 
Between  the  times  of  infection  and  the  appearance  of  the 
smut  masses  in  the  panicle  no  signs  of  the  disease  are  seen 
without  the  aid  of  the  microscope. 

The  smut  can  be  prevented  by  the  use  of  clean  seed, 
obtained  either  from  clean  fields  or  by  disinfecting  the 
seed  by  the  hot  water  (58°  C.  (135°  F.)  for  10  to  15  minutes) 
or  formalin  methods. 

CORN,  TEOSINTE 

Smut^^'^  (JJstilago  zea  (Beckm.)  Ung.).  —  Corn  smut  is 
well  known  to  every  farmer,  occurring  wherever  the  corn 
plant  is  grown,  as  black,  pulverulent  masses  most  conspicuous 
upon  the  ear  and  tassel.  The  damage  in  1917  is  estimated  at 
108,000,000  bushels.  In  Iowa  a  loss  of  two-thirds  of  the  crop 
was  at  one  time  reported. 

Corn  smut  is  first  mentioned  in  literature  in  1754,  and 
the  first  record  of  it  in  America  is  in  North  Carolina  in 
1822.     Experiments  looking  to  its  prevention  were  made 


284 


Diseases  of  Economic  Plants 


as  early  as  1760.  The  disease  may  attack  any  part  of  the 
plant  at  any  age,  —  leaves,  stalks,  aerial  roots,  ears,  tas- 
sels, —  provided  only  that  they  be  still  in  tender  growing 
condition,  not  mature  and  hard. 

The  first  s>nnptom 
is  a  pale,  glistening, 
swollen  area  covered 
with  a  white  mem- 
brane, which  soon  ap- 
pears black  owing  to 
matured  spores 
within.  The  mem- 
I3  r  a  n  e  eventually 
bursts,  loosening  a 
powdery,  dry,  black 
m  ass  of  spores 
through  which  fibrous 
veins  of  the  corn 
plant  still  penetrate. 
It  has  ])een  conclu- 
sively demonstrated 
that  the  causal  fungus 
is  not  conveyed  to 
the  new  crop  in  the 
seed,  as  is  the  case 
with  so  many  other 
smuts,  and  that  there- 
fore no  form  of  seed 
treatment  is  of  value 
for  its  prevention. 

It  has  been  clearly 
shown  that  infection 
is  produced  by  the 
spores  which,  under 
suitable  conditions  of  moisture,  fall  upon  any  tender  part  of 
the  corn  plant.  The  silks  furnish  the  requisite  conditions, 
and  it  is  through  them  that   ear  infection  occurs.     The 


Fig.  148.  —  Corn  smut  upon  the  ear. 
Original. 


Cereals 


285 


sheaths  of  the  leaves  hold  water,  and  inclosing  as  they  do 
the  tender  growing  portion  of  the  stem,  are  admirably  suited 
to  infection.  Since  infection  cannot  occur  without  moisture, 
weather  conditions  are  of  predominating  influence. 


Fig.  149.  —  Smut  upon  sweet  corn  tassels.    After  Jackson. 


The  longer  the  crop  grows,  the  longer  the  period  of  sus- 
ceptibility is  maintained.  Thus  a  late-planted  crop  in  In- 
diana showed  half  as  much  infection  as  a  crop  which  was 


2S6  Diseases  of  Economic  Plants 

planted  earlier,  chiefly  because  it  was  exposed  to  contagion  | 

only  about  half  as  long.  Moisture  and  richness  of  soil  , 
predispose  to  disease  by  increasing  growth  and  giving  a  J 
greater  number  of  susceptible  points  of  attack.  Corn  thickly  j 
planted  is  more  liable  to  infection  because  ventilation  is  j 
restricted,  and  thus  a  more  humid  atmosphere  is  maintained 
around  the  plants.  I 

It  has  been  shown  that  corn  smut  can  be  reduced  by         j 
spraying  with  Bordeaux  mixture,  but  the  saving  does  not         ] 
warrant  the  expense.    To  go  through  the  field  several  times         ■ 
during  the  season  and  cut  out  and  burn  all  the  developing 
smut  masses  that  can  be  seen,  thus  to  destroy  the  spores  and         : 
prevent  the  continued  spread  of  the  disease,  is  recommended,         j 
but  the  actual  utility  of  such  practice  has  not  been  demon- 
strated, though  it  is  probable  that  this  practice  continued 
yearly  would  result  in  continued  diminution  of  smut.     The 
use  of  the  silo  in  which  the  smut  spores  are  rendered  non- 
viable tends  to  lessen  the  amount  of  smut.    The  smut  fungus 
can  live  and  even  increase  in  manure.     Therefore  live  smut 
spores  may  infest  the  manure  pile  and  thereby  increase  the 
disease  in  fields  to  which  such  manure  is  applied.    The  smut 
itself,  contrary  to  popular  belief,  is  poisonous  to  stock  only 
under  very  rare  and  exceptional  conditions,  so  rare  as  to  be         j 
practically  negligible.     Fresh  smut  balls  that  have  not  yet 
turned  dark  are  edible,  and,  prepared  as  mushrooms,  are         , 
delicious.  I 

Head-smut  (Sphacelotheca   reiliana   (Kuehn.)    Clint.).  — 
This   smut,    identical   with   that   of   sorghum,    occasionally 
occurs  upon  corn  and  is  somewhat  more  injurious  though  less         j 
common  than  the  usual  corn  snuit.    It  cannot  be  controlled         | 
by  seed  treatment.  ' 

Corn  Ear  Rots  ^^^  ] 

Four  types  of  ear  rot,  due  to  four  distinct  diseases,  are  I 

described  below.     In  the  aggregate  the  loss  from  these  is  | 

enormous,  constituting  as  it  does  10  per  cent  or  more  of  a  \ 

crop  annually.     Infection  comes  from  definite  species  of  i 


Cereals 


287 


fungi,  and  is  not  cornparable  to  ordinary 
molding  of  dead  organic  matter  by  fungi 
of  varying  kind. 

Dry-rot  (Diplodia  zece  (Schw.)  Lev. 
and  Diplodia  macrospora  Earle) .  —  This 
is  one  of  the  very  widespread,  dry  ear 
rots  of  corn  variously  known  to  growers 
as  mold,  mildew,  rot,  dry-rot,  etc. 

Though  the  disease  is  really  present 
soon  after  silking,  and  even  much  earlier 
from  root  infection,  it  is  not  usually 
recognized  until  husking,  when  a  whitish 
covering  of  the  kernels  within  the  husk 
is  noted.  This  white  mycelium  also 
forms  dense  masses  between  the  indi- 
vidual grains,  among  the  husks,  and  over 
the  cob.  The  grains  on  the  affected  ear 
are  shrunken,  loosely  attached,  light  in 
weight,  darker  in  color,  and  more  brittle 
than  those  of  a  healthy  ear.  Upon 
breaking  open  an  ear,  very  small  black 
pycnidia  may  be  seen  embedded  in  the 
white  masses  of  mycelium,  especially  at 
the  bases  of  the  kernels.  Diseased  ears 
left  in  the  field  may  develop  these  pyaii- 
dia  in  such  abundance  as  to  make  the 
grains  black. 

Much  of  the  food  value  of  the  corn  is 
lost,  owing  to  the  consumption  of  starch 
within  the  grain,  as  well  as  to  the  pre- 
vention of  starch  storage.  The  germi- 
nating power  of  the  grain  is  also  lost. 

Upon  the  stalks  the  fungus  first 
appears  as  very  small  dark  specks  under 
the  rind,  near  the  nodes,  and  at  broken 
places,  usually  in  over-wintered  stalks. 
Three-year-old   stalks  have   been  found 


Fig.  150.  —  Young 
ear  of  com  inocu- 
lated in  the  silk 
with  Diplodia.  Af- 
ter Burrill  and 
Barrett. 

bearing  pycnidia. 


288 


Diseases  of  Economic  Plants 


Although  the  green   stalks  are  not  naturally   susceptible, 
the  shanks  are  particularly  so. 

The  causal  fungus  gains  entrance  to  the  ears  from  attacked 
stalks  which  bear  them,   and   these  are  in  turn   infected 


^^ 

fl.^Jf,^,.^^ 

te^^'"^ 

B^'^**^*--^^^ 

^^fe';'-ii^H 

W^ 

B     '''1 

mt 

^^^k             '>^H 

mm 

%f 

Fio 


151.  —  Diplodia  on  old   si 
Burrill  and  Barrett. 


inks.     After 


through  the  roots  from  the  soil.  Ears  are  also  invaded 
through  the  silks  by  wind-borne  spores,  which  come,  in  part, 
from  diseased  ears,  but  more  largely  from  diseased  stalks 
left  in  the  field. 


Cereals 


289 


Any  method  of  reducing  the 
amount  of  infective  trash,  par- 
ticularly old  stalks  near  or  in  the 
fields,  aids  in  control  of  this  pest. 
Practically,  this  means  to  take 
out  of  the  field  and  destroy  all 
rot-infected  ears  and  to  cut  in- 
fected stalks  low  and  haul  them 
away  or  burn  them.  It  is  still 
better  to  practice  such  rotation 
that  corn  will  not  follow  corn 
within  two  years. 

Dry-rot  (Fusarium  sps).  — 
Upon  the  ears  this  disease  ap- 
pears as  a  dense,  felted,  white 
mycelium,  extending  between 
the  kernels  to  the  cob.  The 
kernels  are  killed  and  their 
starch  partly  consumed. 

A  second  Fusarium 
characterized  by  a  deep 
to  red  color  noted  on  the  ear 
when  the  husks  are  removed. 
The  kernels  are  brittle  and 
the  starchy  portion  within  is 
powdery. 

A  third  Fusarium  disease 
causes  less  complete  destruction 
of  the  ear  than  the  preceding; 
often  only  a  few  scattered  ker- 
nels are  affected.  The  mycelium 
is  white  and  sparse.  A  cob- 
rot  ^^^  due  to  Coniosporium 
softens  the  cob  without  mate- 
rially injuring  the  grain. 

Root-rot,   stalk-rot  ^i"^-  504.  506,  528 
first  record  of  root  and  stalk-rots  of 


IS 

pink 


Fig.  152.  —  Corn  mold  caused 
by  Fusarium.  After  Burrill 
and  Barrett. 

(Fusarium  sps.).  —  The 
corn  was  made  in  1907  by 


290  Diseases  of  Economic  Plants 

Selby,  in  Ohio.  In  1914,  Pammel,  in  Iowa,  called  attention 
to  a  serious  root-rot  of  corn  caused  by  a  Fusarium.  The 
disease  is  now  known  to  prevail  generally  throughout  the 
corn  belt  both  in  the  South  and  the  North.    Though  no  ac- 


FiG.  153.  —  Rotten  stalk  and  the  nubbin  re- 
sulting.    After  Hoffer. 

curate  estimate  has  been  made  of  the  amount  of  damage,  it 
is  known  that  the  loss  is  large. 

Among  the  symptoms  are:  1.  Poor  stands  due  to  missing 
hills,  caused  by  defective  germination.  2.  Weak  and  stunted 
seedlings,   many   of  which  may  eventually   die.     Stunted 


Cereals  291 

plants  show  decayed  roots  and  purplish-brown  discolored 
stalks  when  split  lengthwise.  3.  Down-stalks  due  to  rotting 
of  the  roots,  so  that  the  plant  falls  over.  4.  Broken  stalks 
due  to  weakening,  chiefly  at  the  nodes,  5.  Barrenness  and 
nubbin  formation.  The  infected  plant  lacks  vitality  to  form 
a  perfect  ear.  6.  Broken  shanks  due  to  rot.  7.  Diseased 
kernels.  The  kernels  may  be  molded  and  cracked,  though 
no  sign  of  disease  may  be  apparent  and  the  infection  or 
weakening  of  the  kernels  shows  only  on  germination.  The 
severity  of  the  attack  depends  upon  the  stage  of  develop- 
ment, the  vigor  and  resisting  power  of  the  corn  plant  as 
determined  by  the  conditions  for  growth  and  development, 
and  by  its  heredity. 

Root-rot  is  caused  by  fungi,  mainly  Fusarium,  and  arises 
chiefly  from  primary  infection,  from  infected  seed,  though  to 
some  extent  from  secondary  infection  in  the  field.  The 
planting  of  infected  seed  is  largely  responsible  for  missing 
hills,  down-stalks,  nubbins,  and  other  signs  of  disease. 

No  infected  corn  should  be  used  for  seed.  To  eliminate  the 
infected  seed,  special  adaptation  and  care  in  using  the  rag- 
doll  tester,  or  the  use  of  special  testers,  devised  by  Hoffer,  is 
necessary,  whereby  the  seedlings  that  show  infection,  when 
less  than  three  inches  in  height,  may  be  recognized  and  the 
ears  from  which  they  originated  discarded. 

Since  the  wheat  scab  organism  (Giberella)  causes  rot  of 
stem  and  shank  of  corn,  corn  so  diseased  increases  the  amount 
of  wheat  scab  in  succeeding  crops. 

Wilt  ^^'^-  ^^^  (Pseudomonas  stewarti  EFS.).  —  This  corn  wilt 
was  first  described  by  Stewart  as  prevalent  in  nearly  all  parts 
of  Long  Island  upon  many  different  varieties  of  sweet  corn. 
In  some  cases  the  entire  crop  was  ruined,  and  20  to  40  per 
cent  of  loss  was  frequent,  though  in  the  majority  of  cases  the 
loss  was  so  slight  as  to  pass  without  notice.  It  has  been 
noted  on  sweet  corn  in  Kentucky  and  Illinois,  but  rarely  on 
field  corn. 

The  diseased  plants  wilt  and  dry  up  much  as  though  from 
lack  of  water,  yet  in  soil  that  is  amply  supplied  with  water. 


292  Diseases  of  Economic  Plants 

While  the  wilting  is  most  likely  to  occur  at  flowering  time, 
it  may  appear  at  any  stage  of  growth  when  the  plants  are 
25  cm.  or  more  in  height.  In  mild  cases  the  lower  leaves 
wilt  first,  while  in  severe  cases  all  wilt  at  one  time.  The 
death  of  the  plant  may  occur  in  four  days  after  the  first 
signs  of  disease,  or  may  be  delayed  a  month,  possil^ly  with 
recovery  and  relapse  intervening. 

The  roots  remain  normal,  l^ut  the  veins  in  the  stems 
appear  as  yellow  streaks,  in  older  cases  black,'  instead  of 
their  normal  color.  Such  stems,  if  cut  crosswise,  shortly 
exude  a  yellow,  viscid  drop  at  the  ends  of  the  veins.  This 
is  the  most  distinctive  character,  and  infallibly  indicates 
the  presence  of  the  wilt.  Death  is  caused  by  the  plugging 
of  the  water  passages  with  this  viscid  substance,  which  con- 
sists mainly  of  bacteria. 

In  the  fields  the  diseased  plants,  representing  young  and 
old  stages  of  infection,  grow  side  by  side  with  normally 
healthy  plants.  Health  and  disease  may  appear,  even  in  the 
same  hill;  yet  there  appears  to  be  no  direct  plant-to-plant 
infection,  nor  any  of  that  centrifugal  spreading  from  a 
diseased  center  that  is  so  noticeable  in  most  wilt  or  soil-borne 
diseases. 

The  causal  organism  is  found  in  the  seed  from  affected 
plants,  and  it  has  been  proved  experimentally  that  such 
seed  carries  the  disease  to  the  offspring. 

As  a  preventive  measure  resistant  varieties  should  be 
selected  for  planting,  and  all  seed  from  plants  which  are  at  all 
diseased  should  be  avoided.  The  disease  may  be  carried  from 
one  locality  to  another  by  any  of  the  means  suggested  under 
soil  diseases,  and  especially  by  manure  infested  with  stalks  of 
diseased  plants. 

Mmor  diseases 

Brown-spot  ^^^  (Physoderma  zexv-maydis  Shaw)  was  first 
noted  in  India  in  1910,  in  Illinois  in  1911.  Its  distribution 
is  shown  in  the  accompanying  map.  (Fig.  154.)  Considerable 
damage  is  done  in  the  region  indicated  by  the  darker  shading, 


Cereals 


293 


but  it  is  hardly  probable  that  this  disease  will  extend  seriously 
or  become  very  destructive,  except  locally,  and  in  very 
humid,  hot  seasons.  In  some  cases,  the  injury  is  as  high  as 
6  to  10  per  cent  of  the  crop.  The  fungus  grows  in  leaf, 
sheath,  and  stem,  rarely  in  the  husks.  Bleached  or  yellow 
spots  about  1  mm.  in  diameter  first  appear,  and  within  a  few 
days  darken,  eventually  becoming  reddish-brown.     Coales- 


FiG.  154.  —  Map  showing  the  distribution  of  Physo- 
derma  zeae-maydis  in  the  United  States.  Broken  lines, 
P.  zeae-maydis  present:  solid  line,  P.  zese-maydis  caus- 
ing damage.    After  Tisdale. 


cence  of  many  spots  may  lead  to  discoloration  of  large  areas 
and  a  rusted  appearance.  These  diseased  areas  are  often  in 
bands  across  the  leaf.  Leaves  are  often  killed.  The  dry 
epidermis  eventually  ruptures  over  diseased  spots  and  the 
dusty,  brown  spores  are  freed.  Diseased  stems  break  easily, 
resulting  in  considerable  lodging  of  the  corn.  General  san- 
itary measures  are  recommended,  chiefly  destruction  of  in- 
fested refuse  and  rotation  of  crops. 


294 


Diseases  of  Economic  Plants 


Blight  ^^'^  (Pseudomonas  sp.).  ■ —  This  disease  was  described 
by  Burrill  in  1889. 

It  shows  chiefly  as  a  dwarfed  condition  which  may  occur 
in  spots  m  the  field,  varying  in  size  from  a  few  square  rods 

to  an  acre  or  more.    The 

affected  plants  finally  turn 
yellow,  and  most  of  them 
die. 

The  lowest  roots  of  dis- 
eased plants,  in  some  cases 
comprising  half  of  the  root 
system,  die.  The  stalk 
near  the  base,  when  split 
lengthwise,  shows  a  uni- 
form, dark  color  which 
also  appears  in  the  upper 
nodes  in  lesser  degree. 

Rust  {Puccinia  sorghi 
Schw.).  —  Corn  rust  seems 
to  have  taken  its  place  in 
literature  in  1815.  It  is 
comparatively  of  slight 
importance,  since  it  does 
not  usually  develop  early 
in  the  season,  though 
in  exceptionally  favorable 
climatic  conditions  it  may 
do  so.  The  brown  sum- 
mer spores  appear  first  in 
linear  sori,  and  the  black 
winter  spores  come  later 
in  the  season.  The  cluster- 
cup  stage  is  found  upon 
the  wood  sorrel  (Oxalis). 
{Helminthosporium  inconspicuum  C. 
blight    gives   a   somewhat    frostbitten    ap- 


FiG.  155.  —  Portion  of  corn  leaf  show 
ing  sori  of  rust. 


Yellow-leaf  ''''  ''' 
&   E.).  — This 
pearance  to  the  plants,  producing  also  a  thin  olive-green 


Cereals  295 

mold  upon  the  lower  sides  of  the  leaves.  Sometimes  only  the 
tips  of  the  leaves  are  affected,  but  usually  whole  leaves  die. 

Yellowish,  elongated  spots  limited  by  the  veins,  sometimes 
covered  with  dark-colored  spores,  are  produced.  The  disease 
is  confined  almost  entirely  to  late-planted  corn,  and  is 
prevalent  during  its  early  growth,  though  it  has  never  been 
reported  upon  seedlings. 

It  is  known  to  cause  nmch  loss  in  Delaware,  New  York, 
and  Connecticut,  and  is  of  widespread  occurrence  in  the 
United  States. 

Chlorosis  appears  to  be  related  to  the  mosaics  in  that  it  is 
transmitted  by  sap  or  by  contact.  It  occurs  also  in  the 
embryo.  Two  species  of  Sclerospora  cause  considerable 
injury  to  corn  in  Italy,  and  have  been  collected  in  the  United 
States.  The  tassel  is  chiefly  affected.  Phyllachora  causes 
damage  to  corn  in  the  warmer  climates.  In  the  Orient  very 
great  loss  is  caused  by  a  downy-mildew  (Peronospora) . 

EMMER,  EINKORN.     See  p.  310. 

KAFIR.    See  p.  307. 

MILLET 

Leaf-spot  ^'"  (Piricularia  grisea  (Cke.)  Sacc).  —  Upon  the 
lower  leaves  the  disease  occurs  as  a  spot  which  is  at  first  dark 
purple  or  reddish,  and  elongated  parallel  with  the  length  of 
the  leaf.  Later  the  center  turns  black  and  finally  straw- 
colored,  bordered  by  a  black  ring  which  merges  into  reddish- 
purple  at  its  outer  edge.  Badly  diseased  leaves  turn  yellow, 
dry  and  shrivel  from  the  tip  toward  the  base,  lessening  the 
fodder  value  and  seed  yield  of  the  plant. 

Smut  (Ustilago  crameri  Koern.).  —  This  smut  infects  the 
individual  flowers  of  the  fox-tail  millets,  destroying  the  lower 
parts  of  the  glumes  and  the  grain.  It  has  been  noted  in  Ohio, 
Minnesota,  Connecticut,  Illinois,  Indiana,  Iowa,  Maine, 
Michigan,  Colorado,  North  Dakota,  and  South  Dakota. 
U.  panici-miliacei  similarly  affects  the  Panicum  millets. 


296 


Diseases  of  Economic  Plants 


The  formalin  treatment,  1  pint  to  40  gallons,  is  applicable 
to  both  of  these  smuts. 

MILO.    See  p.  307. 


OAT 

Loose-smut  ^-^'  ^^^"^"^^   {Ustilago  avenos.   (Pers.)    Jens.).  — 

Under  the  name  "smut,"  "blackheads,"  etc.,  this  disease  is 

known  wherever  oats  are 
grown.  Grain  and  more 
or  less  of  the  chaff  are 
replaced  by  a  powdery, 
black  mass,  which  shat- 
ters out  as  it  ripens,  leav- 
ing later  only  the  naked 
branches  of  the  panicle. 
Usually  all  the  spike- 
lets  of  a  head  and  all 
the  heads  of  the  affected 
plant  are  smutted. 
There  is  considerable  dif- 
ference in  the  resistance 
offered  by  different  va- 
rieties, but  in  view  of  the 
perfect  protection  af- 
forded by  proper  treat- 
ment this  is  of  little 
significance. 

The  damage  caused  by 
smut  is  commonly  under- 
rated. In  1884  Arthur 
in  New  York  by  actual 
count  found  the  oat 
smut  to  constitute  from 
8.5  to  10  per  cent  of  the 
Fig.  156. -Loose  smut  on  oats.  After  ordinary  crop.  By  ac- 
Jackson.  tual     count     of    nearly 


Cereals  297 

11,000  heads  Plumb  in  1886  determined  the  amount  of  smut 
to  be  8.4  per  cent;  in  some  fields  he  found  as  high  as  20,  28, 
and  even  30  per  cent.  Kellerman  and  Swingle,  counting 
smutted  heads  in  Kansas,  found  different  fields  to  have  8, 
15.3,  and  18.3  per  cent  of  smut,  while  single  portions  of  a 
field  showed  as  high  as  30  per  cent.  The  loss  in  this  country 
in  1917  was  estimated  as  approximately  91,000,000  bushels. 

The  reasons  for  underestimation  of  oat  smut  are:  1,  the 
dwarfing  of  many  of  the  affected  plants,  which  thus  re- 
main unnoticed  by  a  casual  glance  over  the  field;  2,  the 
fact  that  many  smutted  panicles  remain  invisible  unless 
unrolled  from  their  enveloping  leaves. 

It  was  proved  as  early  as  1858  that  infection  can  occur 
only  upon  the  very  young  oat  plant;  that  older  plants  are 
immune.  It  was  later  determined  by  Brefeld  that  the 
plants  are  immune  after  the  leaves  have  protruded  1  cm. 
beyond  the  leaf  sheath.  From  this  and  other  experiments 
it  follows  that  practically  all  infection  comes  from  smut 
spores  which  are  upon  the  seeds  when  they  are  planted. 
These  germinate,  producing  sporidia  which  infect  the  young 
plant.  The  fungus  develops  in  these  plants  throughout  the 
season  without  conspicuous  effect  until,  at  blossoming  time, 
the  fungus  seeks  the  ovaries  and  the  glumes  and  appears 
again  as  the  familiar  black  spore  masses. 

Any  treatment  which  kills  the  spores  upon  the  seed  with- 
out materially  injuring  the  seed  itself  results  in  a  clean  crop. 

The  copper  sulfate  treatment  endangers  germination  of 
oats.  The  hot  water  treatment  is  less  convenient  than  the 
formalin  treatments  which  are  thoroughly  satisfactory. 
See  p.  270. 

Covered-smut  {Ustilago  levis  (K.  &  S.)  Magn.),  —  This 
differs  from  the  loose  smut  in  the  less  complete  destruction  of 
the  flowers  and  in  its  less  dusty  spore  masses,  which  are  also 
blacker  than  in  the  loose  smut.  The  smut  masses  are  usually 
limited  to  the  parts  within  the  flowering  glume  and  the  palet 
or  to  the  bases  of  these. 

The  treatment  is  that  given  for  loose  smut. 


298 


Diseases  of  Economic  Plants 


Black-stem-rust  {Puccinia  graminis  avence  E.  &  H.).  — 
The  black-st em-rust  on  oats  shows  but  sUght  differences  from 
the  black-stem-rust  of  wheat,  but  it  is  racially 
distinct  (see  p.  277)  and  a  field  of  one  of  these 
crops  may  be  badly  affected  by  its  fungus, 
while  adjacent  fields  of  the  other  crop  show 
no  rust  or  indication  of  infection  such  as  they 
might  be  supposed  to  do  were  the  two  rusts 
identical. 

As  with  the  wheat  black-stem-rust,  its  at- 
tacks fluctuate  greatly  in  abundance  and 
destructiveness  from  year  to  year. 

Crown-rust  (Puccinia  coronata  Cda.). — 
This  rust  is  found  only  upon  species  of  oats 
and  closely  related  grasses  and  in  the  telial 
stage  clearly  differs,  even  to  the  naked  eye, 
from  the  oat  rust  mentioned  above. 

It  occurs  upon  oats  in  practically  all  fields 
but  is  more  injurious  in  its  southern  range. 
The  damage  is  not  serious,  or  very  rarely  so. 

The  cluster-cup  stage  is  known  to  grow 
upon  the  common  buckthorn  {Rhamnus  cath- 
artica)  and  the  lance-leaved  buckthorn  {R. 
lanceolatus) .  The  yellow  uredinial  stage  is 
most  conspicuous.  Later  the  black  telia  ap- 
pear under  the  epidermis  as  long  streaks 
which,  unlike  most  rusts,  do  not  rupture  the 
epidermis. 

Marked  varietal  resistance  is  shown.  In 
California  black  oats  are  reputed  to  be  less 
subject  to  rust  than  white  oats.  In  the 
North,  the  White  Russian  is  said  to  be  resist- 
ant, while  in  the  South,  the  red  oats  resist 
attack. 
Minor  diseases 

Scab.   See  wheat.    Leaf-spot  (PhijUosticta  sp.).  —  Browned 
or  reddened  leaves,  with  the  black  pycnidia  profuse  upon  the 


Fig.  157.— Cov- 
ered-smut on 
oats.  After 
Jackson. 


Cereals  299 

affected  surfaces,  sometimes  so  abundant  as  to  lend  a  blackish 
hue  to  the  leaf,  comprise  the  diagnostic  symptoms  of  this 
malady.    Eventually  the  leaves  are  killed. 

Blight  ^^^' ^^''  (Pseudomonas  avence  Manns).  —  A  disease 
prevalent  throughout  the  Eastern  and  Central  States  was 
attributed  to  bacteria  by  Galloway  and  South  worth  in  1890. 
It  appears  when  the  plants  are  only  about  10  cm.  high,  first 
causing  the  leaves  to  turn  brown  and  die  at  the  tips,  then 
throughout  their  length.  The  affected  plants  revive,  but 
are  so  reduced  in  vigor  as  to  prevent  effective  stooling,  and 
a  loss  of  from  35  to  75  per  cent  of  the  crop  commonly 
occurs. 

The  disease  was  carefully  investigated  by  Manns,  who 
claims  that  it  is  caused  by  the  symbiotic  action  of  two  species 
of  bacteria,  a  Pseudomonas  and  a  Bacillus. 

Manns  describes  the  disease  as  follows: 

The  preliminary  effect  is  yellowing  of  the  leaf,  beginning 
either  as  small,  round  lesions  on  the  blade,  or  as  long,  streak- 
like lesions  extending  throughout  the  blade  and  even  the 
whole  length  of  the  culm  and  blades.  Occasionally  it  begins 
at  the  tips  and  works  back  into  the  culm;  again  the  upper 
leaves  often  break  down  due  to  a  weakened  condition  of 
the  plant  from  defoliation  below. 

The  ultimate  symptoms,  wherever  the  disease  has  made 
much  progress,  are  partial  or  general  collapse  of  the  leaves, 
which  take  on  a  mottled  to  almost  red  color. 

It  prevails  from  New  England  to  Georgia,  and  from  the 
Atlantic  to  Indiana  and  Illinois.  The  damage  in  Ohio  has 
been  estimated  at  from  14  to  37  per  cent  of  the  crop.  Rain 
and  moisture  favor  it. 

When  prevalent,  the  soil  may  become  infested  as  in  typical 
soil  diseases.  The  only  hope  seems  to  rest  in  resistant 
strains. 

Halo-blight  (Bacteria).  —  Oval,  chlorotic  areas  1-2  cm.  in 
diameter,  bordering  a  minute,  sunken,  dead  center,  occur 
in  the  leaf.  Stripe-blight  (Bacteria).  —  The  diseased  tissues 
are  water-soaked,  translucent,  with  an  abundant  exudate  and 


300  Diseases  of  Ecoiiomic  Plants 

no  halo.  The  spot  is  long  and  narrow,  between  the  veins. 
Anthracnose  {Colletotrichum  cereale).  —  The  effect  of  this 
disease  upon  oats  is  similar  to  that  described  for  rye.  Yellow- 
leaf  {Helminthosporium  inconspicuum  C.  &  E.  var.  brittani- 
cum  Grove).  —  Oat  leaves  turn  yellow  and  develop  dark, 
brown,  spore-bearing  spots.  Little  is  known  as  to  its  severity 
or  prevention.  Powdery-mildew.  See  wheat.  Ergot  occurs 
but  rarely  on  oats. 

RICE  ''' 

Blast,  rotten-neck  ^^^  (Piriculana  oryzoe  Cav.).  —  This  is  a 
world-wide  rice  disease,  which  in  Italy  is  controlled  by  the 
use  of  resistant  varieties.  It  has  probably  been  present 
for  many  years  in  American  rice  sections,  but  did  not  become 
of  serious  economic  importance  until  about  1895.  What 
seems  to  be  the  same  disease  occurs  upon  crab  grass,  and 
apparently  infection  may  come  from  this  host.  It  is  reported 
from  South  Carolina  and  Louisiana,  also  from  Texas,  where 
it  has  been  serious.  The  disease  occurs  upon  upland  as  well 
as  irrigated  fields. 

The  most  characteristic  symptom  consists  of  lesions  at 
the  sheath  nodes  just  over  the  joints  of  the  stem,  at  the 
region  where  the  stem  comes  to  be  the  axis  of  the  head 
(the  ''neck  region")  and  at  the  points  where  the  blades  of 
the  leaves  join  their  sheaths,  appearing  first  as  very  small, 
water-soaked,  sunken  spots  on  the  node  of  the  sheath.  Spots 
upon  the  neck  are  not  water-soaked,  and  the  skin  does  not 
rupture  until  the  head  breaks  off.  Later  the  spot  becomes 
brownish  or  black,  and  similar  discoloration  runs  upward  and 
downward.  The  affected  stem  tissue  gradually  extends 
laterally,  shrinks,  and  dies,  cutting  into  or  through  the  joint, 
which  results  in  an  open  wound.  The  region  above  the 
wound  becomes  pale  and  dies. 

Upon  young  plants  leaf  spots  occur,  first  brown  with  ashen 
center,  later  coalescing  and  taking  th(>  whole  leaf.  If  the 
attack  is  early,  the  grain  does  not  fill  at  all;  if  late,  it  may 


Cereals 


301 


partially  fill.    The  dead  portion  of  the  plant  may  bleach  or 
darken  according  to  environment,  resulting  in  varied  char- 
acters in  later  stages  of  the  disease.    In  70  per  cent  of 
the  cases  examined  by  Metcalf  the  lowest 
joint   of  the  rachis  was  affected,  and  in 
consequence  the  heads  broke  off  at  this 
point.     This    gives  rise  to   the   common 
name  "rotten-neck,"  but  since  the  char- 
acter is  not  universal,  the  name  is  not  an 
appropriate  one. 

The  chief  damage  results  from  the  failure 
of  the  grain  to  fill  on  the  diseased  stalks. 
An  early  attack  may  render  a  crop  entirely 
worthless.  Plants  attacked  later,  yield 
some  grains  which  are  of  poor,  light  qual- 
ity, easily  broken  or  blown  away,  and  con- 
sequently largely  lost  in  threshing  and 
milling.  The  variation  in  size  of  the  grain 
also  largely  depreciates  the  quality.  Many 
of  the  heads,  especially  the  heavier  ones, 
fall  off,  and  some  fields  show  at  least 
one-third  of  the  crop  thus  left  upon  the 
ground. 

The  Rice  Committee  of  the  Agricultural 
Society  in  South  Carolina,  March,  1904, 
estimated  the  loss,  up  to  that  time,  to  be 
very  nearly  $1,000,000.  Depreciation  in 
land  values,  necessitating  abandonment  of 
land,  is  a  significant  item  of  charge  against 
this  disease. 

The  chief  hope  lies  in  the  use  of  resistant 
varieties.  Withholding  nitrogenous  ferti- 
lizers and  removal  of  infective  trash  by 
burning  are  good  sanitary  measures. 

Green-smut  (Usfilaginoidea  virens  (Cke.)  Tak.).  —  This 
grain  disease,  though  partaking  of  the  appearance  of  a  true 
smut,  is  in  reality  more  closely  related  to  the  ergot  of  rye. 


Fig.  158.  — Rice 

blast.    After 
Fulton. 


302 


Diseases  of  Economic  Plants 


The  grains,  usually  only 
larged,  spherical,  5  mm. 


few  in  each  head,  become  en- 
more  thick,  and  coated  with 
a  dark  green  powder.  Some- 
times a  yellow  color  prevails 
instead  of  the  green.  In  sec- 
tion the  interior  is  seen  to  be 
filled  with  a  compact  white 
mass  bordered  by  a  brownish 
yellow  zone,  then  by  the  green 
coating. 

Though  the  disease  has  been 
known  in  Louisiana  for  ten  or 


Fig.     159. — -Rice     showing 
"  green-smut."   After  Fulton. 

more  years,  and  is  present  to 
some  extent  in  most  fields,  it  is 
not  considered  serious,  since 
rarely  more  than  0.25  per  cent 
of  the  heads,  and  only  a  few 
grains  per  head,  are  affected. 

Black-smut  ^^"  (Tilletia  horrida 
Tak.).  —  A  dark,  unsalable  flour, 
made  from  rice  in  the  region  of 
Georgetown,  S.  C,  was  reported 
in  1898.  Anderson  found  that 
many  heads  of  rice  from  these 
fields  bore  as  much  as  25  per 
cent  of  smutted  grains. 

This  smut  was  probably  imported  from  Japan  in  infected 
seed,  but  due  to  the  immediate  action  of  Anderson  and 
Walker  the  pest  seems  to  have  been  completely  stamped 


Fig.    160.  —  Rice    showing 
black-smut.    After  Fulton. 


Cereals 


303 


out  in  South  Carolina  within  the  first  few  years  after  its 
advent.  No  reports  whatever  of  its  presence  there  have 
been  made  since  1903.  It  has  since  entered  the  United  States 
through  Louisiana. 

The  smut  closely  resembles  the  stinking  smut  of  wheat. 
The  affected  ovaries  or  grains  are  transformed  into  smut 
masses  which  remain  within  the  glumes,  and  so  resemljle  the 
normal  grains  as  often  to  be  mistaken  for  them.  The  fungous 
mycelium  grows  within  the  stem  tissue  of  the  diseased  plant 
and,  as  is  the  case  with  wheat  bunt,  infection  probably 
occurs  in  the  seedling  stage,  the  fungus  remaining  unnoticed 


Fig.  161.  —  Three  rice  spikelets:  A,  normal; 
B,  smutted;  C,  glumes  partly  torn  away  ex- 
posing the  spore  mass.    After  Anderson. 


until  its  presence  in  place  of  the  grain  is  disclosed  as  a  black 
spore  mass. 

The  disease  can  be  controlled  by  the  method  which 
stamped  it  out  in  South  Carolina;  that  is,  by  the  formalin 
treatment. 

Damping-off.  —  Two  forms  of  damping-off  of  seedlings 
are  known : 

1.  Rice,  not  covered,  but  simply  flooded  with  water, 
frequently  shows  soft  rot  of  the  shoot  in  very  young 
seedlings. 

2.  Covered  rice  often  shows  damping-off  spots  just  above 
the  surface  of  the  ground. 


304  Diseases  of  Economic  Plants 

The  causes  of  these  rots  have  not  been  fully  studied,  but 
they  are  probably  due  to  fungi  or  bacteria  or  both. 

Minor  diseases 

Spotted-blight  (Macrosporium  sp.).  —  Small  black  spots 
of  mold  upon  poorly  filled  grains  sometimes  occur,  occasion- 
ally affecting  field  areas  of  considerable  size. 

Speck,  pip  (Saprophytic  fungi  and  bacteria).  —  The  grain 
in  some  instances  bears  one  or  more  discolored,  often  sunken, 
circular  areas,  1-3  mm.  in  diameter,  bounded  by  dark  mar- 
gins with  gray  or  pale-buff  centers  and  often  with  a  minute 
dark  spot  in  the  very  center.  In  other  cases  the  grain  is 
shriveled  and  distorted  without  any  definite  spot.  The 
interiors  of  the  grains  are  chalky  and  brittle,  and  of  such 
inferior  quality  as  to  be  largely  depreciated  in  value.  Not 
infrequently  from  10  to  25  per  cent  of  the  grain  is  affected, 
and  in  some  cases  nearly  100  per  cent.  The  germinating 
power  is  much  reduced. 

The  disease  is  caused  by  the  invasion  of  saprophytic  fungi 
or  bacteria  into  wounds  caused  by  sucking  bugs.  Methods  to 
control  these  insects  have  not  been  thoroughly  worked  out. 

Rust  (Physiological).  —  The  leaves  die  gradually,  begin- 
ning with  the  tips  of  the  lower  ones.  Red  spots  and  streaks 
usually  appear  before  the  leaves  lose  their  green  color.  The 
roots  are  poorly  developed,  the  plants  dwarfed,  and  the  heads 
small  and  light. 

RYE 

Ergot  {Claviceps  purpurea  (Fr.)  TuL). — Ergot  is  widely 
known  as  a  black  or  purplish  body,  several  times  larger 
than  the  seed  of  the  affected  plant,  which  displaces  the 
ovary  or  grain.  Ergot  occurs  commonly  upon  rye  and 
many  other  species  of  grass,  as  wheat-grass,  wild  ryes,  blue- 
joint,  Kentucky  blue-grass,  Canada  blue-grass,  red-top, 
timothy,  and  rye-grass.  Of  the  last  named,  one  farmer 
reports  1000  tons  of  hay  so  badly  affected  as  to  be  worthless. 
Ergot  is  occasionally  injurious  on  wheat. 


Cereals  305 

This  disease  is  caused  by  the  attack  of  a  fungus  upon  the 
ovary  while  the  plant  is  in  bloom.  The  fungus  invades 
and  consumes  the  ovary  and  replaces  it  with  the  ergot,  which 
consists  of  a  dense  mass  of  tangled,  interwoven  mycelium, 
a  sclerotium.  Ergots,  when  mature  and  under  suitable 
conditions,  germinate,  sending  forth  several  stalks  each, 
with  club-shaped,  knobbed  tops.  From  these  the  spores 
issue  to  infect  susceptible  plants  then  in  blossom.  For 
some  days  the  fungus  spreads  from  blossom  to  blossom  by 
means  of  other  spores,  and  each  infected  ovary  results  in 
another  ergot. 

Loss  to  the  grain  and  the  damage  to  the  plant  are  slight. 
Chief  injury  from  ergot  arises  from  its  effect  upon  cattle 
that  are  fed  ergotized  grain  or  graze  upon  badly  infected 
grass.  Animals  become  emaciated  and  rough-haired  as  the 
result  of  continuous  feeding  of  ergot.  Further  symptoms  of 
ergot  poisoning  are  tardy  circulation  in  the  extremities, 
gangrenous  sores  upon  the  teats  or  mouth,  and  sloughing  off 
of  parts  of  the  tail,  ears,  or  hoofs.  Abortion  may  also  follow 
as  an  additional  effect. 

Fields  should  be  examined  for  the  presence  of  ergot.  If 
large  quantities  are  found,  the  grass  should  not  be  used  for 
hay  or  pasture.  Ergot  can  be  lessened  b}^  cutting  susceptible 
grasses  about  flowering  time,  thus  checking  the  spread  of  the 
fungus.  Badty  infested  hay  lands  should  be  burned  over  to 
destroy  sclerotia ;  roadside  grasses  should  be  cut  often  enough 
to  prevent  the  formation  of  ergot,  and  seed  should  be  exam- 
ined to  prevent  the  spread  of  ergot  through  this  means. 
Seed  may  be  freed  of  ergot  by  immersion  in  a  20  per  cent 
solution  of  common  salt,  which  will  float  the  ergot  to  the 
surface. 

Black-stem-rust  (Puccinia  graminis  secalis  E.  &  H.).  — 
The  description  given  in  connection  with  wheat  applies 
here. 

Brown-leaf -rust  {Puccinia  dispersa  E.  &  H.).  —  This 
rust  bears  a  very  close  resemblance  to  the  rust  caused  by 
Puccinia  triticina  upon  wheat,  but  in  careful  inoculation  ex- 


306 


Diseases  of  Economic  Plants 


periments  it  has  been  impossi- 
ble to  infect  one  of  these  hosts 
from  the  other.  It  is  invari- 
ably present  where  rye  is 
grown  and  is  particularly 
abundant  in  the  Southern 
States,  though  notwithstand- 
ing its  universal  presence  it  is 
not  destructive.  The  uredi- 
nial  mycelium  remains  alive 
in  the  South  and  continues  to 
produce  spores  during  winter 
in  the  leaf,  as  it  probably 
does  in  colder  climates  as  well. 
It  is  possible  that  it  is  in  this 
way  carried  from  season  to 
season  by  volunteer  rye  in 
the  fields.  The  cluster-cup 
stage  occurs  upon  a  member 
of  the  Borage  family,  but  has 
never  been  found  occurring 
naturally  in  America. 

Stem-smut  ^-^'  '"^"^  {Urocystis 
occulta  (Wallr.)  Rab.).  —  Un- 
like many  of  the  cereal  smuts 
the  stems  and  leaves  as  well 
as  the  floral  parts  are  affected. 
It  may  be  recognized  by  the 
usual,  dusty,  black  spores, 
which  occur  especially  at  the 
joints.  While  this  disease 
does  not  directly  attack  the 
grain,  it  does  diminish  the 
yield  by  weakening  the  plant. 
Loss  from  25  to  40  per  cent  is 
reported  in  Minnesota,  60  per 
cent  in  Australia.     Seedlings  may  be  infected   from  spores 


Fig.  162.  —  Head  of  rye  attacked 
by  anthracnose.  After  Manns. 


Cereals 


307 


in  the  soil.  When  serious,  the  formalin  treatment  combined 
with  crop  rotation  should  be  employed. 

Anthracnose  ^-^  (Colletotrichum  cereale  Manns).  —  A  serious 
disease  of  cereals  and  other  grasses,  chiefly  rye,  wheat,  oats, 
timothy,  blue-grass,  red-top,  and  orchard  grass,  was  dis- 
covered by  Selby  and  Manns  in  1908. 

It  is  a  destructive  pest  of  very  general  distribution,  being 
found  in  all  the  fields  examined  in  Ohio.  In  one  field  it  is 
estimated  to  have  reduced  the  yield  from  75  to  25  bushels, 
and  it  is  assigned  as  a  prominent  cause  of  shrivehng,  such 


163.  —  Normal  rye  kerneLs  and  shriveled   ones 
due  to  anthracnose.     After  Manns. 

as  is  of  ten  ■  attributed  to  rust,  as  well  as  of  whitening  and 
blighting  of  plants  preceding  ripening.  Parts  of  the  head 
above  the  points  of  attack  die.  The  portion  of  the  head  that 
is  killed  is  a  total  loss,  and  the  general  decrease  in  vigor  of 
the  plant  results  in  shriveled,  light  grains.  Upon  stalks  and 
leaf  sheaths,  beginning  at  the  ground  and  extending  over 
several  internodes,  the  acervuli  may  be  so  numerous  as  to 
cause  blackening. 

No  remedy  is  known. 

Powdery-mildew,  Yellow-stripe-rust  and  Scab.  See  wheat. 

Stripe-disease  and  Stripe-blight.    See  barley. 

SORGHUM,  SUDAN-GRASS,  KAFIR,  MILO 

Blight  (Bacillus  sorghi  Burr.).  —  This  blight  was  studied 
by  Burrill  in  1883  and  described  in  1887.    It  prevails  upon 


308  Diseases  of  Economic  Plants 

sorghum,  broom  corn,  Kafir  corn,  and  Milo  maize,  and 
has  been  noted  in  IlHnois,  Kentucky,  Iowa,  Louisiana, 
Ohio,  Michigan,  Nebraska,  West  Virginia,  and  District 
of  Columbia,  often  in  serious  form.  The  chief  character 
is  irregular-shaped,  elongated  blotches  of  red,  at  first  faint 
orange,  upon  the  leaves  and  leaf  sheaths,  sometimes  limited 
by  the  veins,  and  always  more  conspicuous  on  the  inner 
than  the  outer  sides.  Smaller  patches  later  blend,  and  the 
affected  parts  die  and  finally  turn  black.  The  lower  sides  of 
diseased  spots  upon  the  leaves  often  bear  red  incrustations, 
resulting  from  the  dr3ang  of  the  exudate  from  within.  The 
roots  show  the  same  discoloration,  and  the  outer  parts  of  the 
rootlets  die  and  become  loose.  If  only  slightly  diseased,  the 
plants  may  attain  normal  size. 

Badly  diseased  roots  are  evidenced  by  the  yellowed  tops 
and  other  signs  of  malnutrition.  In  advanced  stages  the 
roots  give  such  poor  anchorage  that  the  plants  may  be  easily 
pulled  from  the  ground. 

Infected  stalks  should  be  burned  and  such  rotation  fol- 
lowed as  to  relieve  the  infested  soil  of  susceptible  crops  for 
several  years. 

Kernel-smuts^'^-  (Sphacelotheca  sorghi  (Lk.)  CI.,  S.  cruenta 
(Kuehn)  Potter) .  —  These  smuts  infest  the  individual  grains 
of  the  panicle,  while  the  head  as  a  whole  remains  nearly 
normal  in  appearance.  The  smutted  grains  are  at  first 
covered  by  a  white,  later  gray,  membrane.  This  membrane 
in  time  becomes  broken  by  the  winter  exposure  and  frees  the 
dark-colored  spores. 

Kernel-smut  was  reported  by  Kellerman  in  1891  as  limited 
to  sorghum  grown  from  imported  seed.  It  was  then  known 
in  the  District  of  Columbia,  Wisconsin,  New  York,  Nebraska, 
and  Kansas.  It  is  widespread  in  Europe,  Africa,  and  Asia, 
and  was  probably  imported  into  the  United  States  upon 
diseased  seed.  It  was  first  recorded  in  the  United  States  in 
1884,  and  is  now  found  in  almost  all  places  where  sorghum  is 
grown. 

According  to   Clinton's  estimates   it  may  prevail  upon 


Cereals 


309 


from  4  to  32  per  cent  of  the  plants.  The  same  investigator 
found  that  the  yield  in  juice  was  lessened  about  30  per  cent, 
owing  to  the  smaller  size  of  the  smutted  plants.  The  damage 
is  particularly  serious  in  kafir  and  broom  corn.    See  p.  283. 

These  smuts  gain  entrance  to  the  host  only  during  the 
very  young  seedling  state,  before  the  plants  appear  above 
ground.  The  mycelium  of  the  causal  fungus  grows  through 
the  plant  until  flowering  time  without  any  indication  of  its 
presence.  At  blossoming  time  the  fungus  seeks  the  ovary, 
destroys  it,  and  becomes  evident  as  smut. 

Disinfection  of  the  seed  by  formalin  is  an  efficient  remedy. 

Head-smut  ^"^^  (Sphacelotheca  reiliana  (Kuehn)  Clinton).  — 

Instead  of   involv- 

ing  the  grains 
singly,  as  in  the 
kernel-smut,  the 
head  as  a  whole  is 
affected.  A  white 
membrane  is  at 
first  present,  but 
this     later     breaks 


open,  exposing  the 


Fig.   164.  —  Three  views  ot  sorghum  kernel- 
smut. 


pulverulent  spore 
mass.  Rarely,  only 
a  portion  of  the  head  is  smutted.  The  spores  soon  weather 
away,  leaving  behind  only  the  veins  of  the  part  involved. 
This  disease  was  first  noted  in  Egypt  in  1868,  and  is  preva- 
lent in  America  only  in  the  Texas  Panhandle.  It  occurs  on 
sorghum  and  to  some  extent  on  corn.     Milo  is  immune. 

The  only  procedure  to  recommend  is  that  employed  for 
corn  smut. 

Anthracnose  {Colletotrichum  falcatum  Went.).  —  Anthrac- 
nose  was  first  seen  in  America  upon  sorghum  in  North 
Carolina,  where  it  did  consideral)le  damage.  It  has  since 
been  reported  from  Louisiana.  The  spots  which  are  more 
prevalent  on  the  lower  leaves  have  very  definite  gray  or  tan- 
colored    centers   which   are   surrounded   by   dark,    reddish- 


310  Diseases  of  Economic  Plants 

brown  rings,  outside  of  which  is  the  ordinary  green  of  the 
healthy  leaf.  As  the  spots  age  they  f requentl}^  grow  together 
and  form  one  large  oblong  area,  sometimes  several  centi- 
meters long.  At  a  late  period  in  the  development  of  the 
disease  the  centers  of  the  spots  are  occupied  by  small  black 
specks,  the  black  acervuli  of  the  causal  fungus. 

TEOSINTE.    See  p.  283. 

WHEAT,  SPELT,  EMMER,  EINKORN 

Black-stem-rust  {Puccinia  graminis  Pers.).  —  Though  in 
earlier  years  this  rust  was  thought  to  grow  indiscriminately 
upon  a  great  variety  of  grasses,  recent,  thorough  study  has 
shown  that  what  was  formerly  regarded  as  one  species  is  in 
reality  a  number  of  races  or  varieties  grouped  under  one 
name.  Collected  on  about  70  species  of  wild  and  cultivated 
grasses  including  wheat,  oats,  rye,  and  barley,  this  rust  is 
now  separated  into  eight  or  more  biologic  forms.    See  p.  277. 

It  is  the  most  serious  of  the  rusts,  of  practically  world- 
wide distribution,  and  causes  more  damage  in  the  Central 
States  than  any  other  rust  except  the  oat  black-stem-rust. 
It  is  injurious  to  oats,  rye,  and  barley  as  well  as  wheat.  The 
damage  done  fluctuates  largely.  The  injury  is  greater  to 
spring  wheat  than  winter  wheat.  In  1916,  the  direct  loss 
was  placed  at  $110,000,000,  in  four  states,  200,000,000 
bushels  in  the  United  States,  and  100,000,000  more  in 
Canada.  Total  loss  of  the  crop  often  results  in  Kentucky, 
Indiana,  Texas,  Michigan,  and  Ohio. 

In  the  spring  or  cluster-cup  stage  upon  the  barberry, 
swollen  spots  are  produced  upon  the  leaves,  fruit,  or  young 
stems.  These  spots  upon  one  side  bear  the  cups  in  abundance 
and  upon  the  other  side  appear  as  pale,  circular  regions  which 
bear  the  small,  black  pycnia. 

Upon  the  wheat  the  rust  shows  first  its  uredinia,  which 
come  later  than  the  uredinia  of  the  orange-leaf-rust,  and 
are  of  more  brownish  tinge.     The  sori  are  most  common 


Cereals  311 

upon  the  stems  and  leaf  sheaths,  more  rare  upon  the  leaf 
blade.  Following  this  stage  the  black  telia  appear  upon  the 
stems  and  leaf  sheaths,  constituting  the  most  conspicuous 
and  predominating  symptom. 

The  damage  by  this  disease  is  due  to  the  inroads  of  the 
fungus  upon  the  green  leaf  tissue,  destroying  the  starch- 
producing  power,  diminishing  the  vigor  of  the  plant,  and 
showing  its  effects  finally  in  the  shrunken,  shriveled  grain. 

Since  this  rust  usually  appears  late  in  the  season,  the 
varieties  of  wheat  that  mature  early  are  likely  to  escape  its 
attack  to  a  greater  extent  than  those  varieties  which  are 
late  in  maturing.  For  a  similar  reason  climatic  or  agronomic 
conditions  which  conduce  to  slow  growth  and  late  maturing 
of  the  crop  favor  the  rust. 

Since  the  common  barberry  (Berberis  vulgaris)  and  its 
varieties,  or  Mahonia  is  necessary  to  the  functioning  of  the 
teliospores,  these  plants  should  not  be  tolerated. ^^^  In  Den- 
mark in  1903  laws  enforced  eradication  of  this  barberry. 
Eleven  years  after  we  read  "'^- 

"  That  black  rust  has  disappeared  gradually,  contemporary 
with  the  barberry  bush. 

"That  the  violent,  destructive  black  rust  attacks,  which 
affected  the  whole  or  most  of  the  country,  with  two  or  three 
years  interval,  have  now  ceased. 

"That  the  weaker  attacks  which  affected  the  grain  and 
grasses  and  especially  the  oats  in  Jutland  are  now  practically 
unheard  of,  or  at  least  come  late  in  the  fall." 

Influenced  by  such  evidence,  in  1918  and  1919  the  Federal 
authorities  and  those  of  many  states,  particularly  in  the 
Middle  States  and  Northwest,  took  energetic  measures  to 
eliminate  the  barberry  and  Mahonia.  Anti-barberry  laws 
were  passed  in  Saskatchewan,  Manitoba,  Canada,  and  many 
states,  notably  in  North  Dakota,  Iowa,  Colorado,  Minnesota, 
Montana,  Nebraska,  South  Dakota,  Wisconsin,  Michigan, 
Illinois.  It  is  clear  from  experimental  evidence  that  the  rust 
does  not  commonly  pass  to  the  next  crop  on  the  seed,  nor 
does  it  commonly  overwinter  in  the  living  host  plants,  except 


312  Diseases  of  Economic  Plants 

in  the  extreme  South.  The  evidence  is  also  to  the  effect  that 
such  rust  as  does  overwinter  in  the  South  does  not  pass  to  the 
North,  but  that  the  main  source  of  infection  in  the  North  is 
from  the  barberry. 

Some  durum  wheats  are  highly  resistant  to  rust,  and 
recently,  by  selection,  the  Kansas  Agricultural  Experiment 
Station  produced  a  bread  wheat  of  the  Crimean  group 
that  under  Kansas  conditions  was  highly  rust-resistant. 
Before  the  rust  problem  can  be  solved  by  breeding  resistant 
plants,  much  fundamental  knowledge  must  be  gained  re- 
garding the  biologic  races  of  the  parasites  and  their  host 
ranges.  Many  wild  grasses  propagate  and  spread  the  rust 
and,  especially  if  they  are  exposed  to  infection  from  the 
barberry,  may  bridge  the  way  to  a  wheat  field.  Prominent 
among  those  grasses  are  wild  barley,  slender-wheat-grass, 
western-wheat-grass,  and  wild  rye  grasses.  Obviously  they 
should  be  kept  down  as  much  as  possible. 

Orange-leaf- rust  (Piiccinia  triiicina  Eriks.).  —  This  rust 
of  wheat  and  possibly  of  several  wild  grasses  is  the  most 
common  and  widely  distributed  of  all  rusts  of  the  United 
States  and  is  especially  injurious  in  the  southern  states.  It  is 
said  by  Carleton  that  it  is  not  only  never  absent  from  the 
wheat  fields  throughout  the  year,  but  that  it  is  sometimes 
abundant  even  in  dry  seasons.  Notwithstanding  its  preva- 
lence its  inroads  upon  the  crop  are  not  usually  serious,  and 
in  no  case  on  record  has  it  caused  shriveling  of  the  grain  such 
as  is  common  from  the  black-stem-rust. 

The  most  conspicuous  character  of  this  rust  is  the  presence 
of  many  orange-colored  sori  upon  the  leaves,  especially  upon 
their  lower  surfaces.  The  grayish  black  telia  are  neither 
so  prominent  nor  so  profuse  as  in  the  black-stem-rust.  Both 
of  these  rusts  possess  the  uredinial  stage,  and  it  is  difficult 
to  distinguish  them  apart  in  this  condition  except  by  the 
microscope. 

As  with  the  rye  orange-leaf -rust,  this  fungus  also  can  winter 
in  its  live  uredinial  mycelium  and  continue  to  bear  uredinio- 
spores  throughout  the  year,  spending  its  entire  existence,  if 


Cereals  .  313 

necessary,  in  this  one  stage  upon  the  single  species  of  host. 
While  no  variety  of  wheat  is  entirely  proof  against  it,  large 
difference  is  shown  in  this  respect,  some  presenting  high 
resistance,  even  under  most  adverse  conditions.  Early 
maturity  is  an  important  factor  in  evading  rust. 

The  following  standard  varieties  are  recommended  by 
Carleton  as  possessing  considerable  resistance  to  the  orange- 
leaf -rust  in  every  part  of  the  country — "Winter  wheats: 
Turkey,  Mennonite,  Pringles  No.  5,  Tieti,  Odessa,  Pringles 
Defiance.  Spring  wheats:  Haynes  Blue  Stem,  Saskatche- 
wan Fife. 

"The  following  varieties  seem  to  be  resistant,  but  have  not 
yet  been  well  established  as  such:  Theiss,  Oregon  Club, 
Sonora,  Diehl  Mediterranean,  Fulcastgr,  Arnolds  Hybrid, 
California  Spring. 

"Some  of  the  hardy  prolific  sorts  not  yet  well  known  in  this 
country,  but  likely  to  be  more  or  less  rust-resistant  after 
thorough  acclimation  and  selection,  are  —  Winter  wheats: 
Prolifero,  Banatka,  Red  Winter,  Nashi,  Tangarotto,  Bearded 
Winter,  Winter  Ghirka,  Budapest,  Crimean,  Yx,  Bellevue, 
Talavera.    Spring  wheats:  Alsace,  Spring  Ghirka. 

"Two  varieties  which  are  quite  susceptible  to  rust,  but 
which  usually  ripen  early  enough  to  escape  the  worst  effects 
of  it,  are:  Early  May  and  Zimmerman. 

"Some  others  not  quite  so  well  known,  but  probably 
worthy  of  trial  as  rust-escaping  sorts,  are  —  Early  Baart, 
Allora  Spring,  Kathia,  Roseworthy,  Japanese  No.  2,  Yemide, 
Canning  Downs. 

"These  last  varieties  are  not  likely  to  withstand  very 
severe  winters,  and  are  therefore  best  adapted  to  southern 
districts,  where  they  may  perhaps  in  time  become  accli- 
mated. Yemide  and  Kathia  are  jn-obably  the  most  hardy 
of  the  six.  Canning  Downs  winter-killed  in  one  trial,  even 
in  Mississippi." 

Yellow-stripe-rust  {Puccinia  glumarum  (Schum.)  E.  & 
H.).  —  This  rust,  which  is  serious  in  Europe  on  wheat  and 
barley  and  less  so  on  rye  and  several  wild  grasses,  was  found  in 


314  Diseases  of  Economic  Plants 

Arizona  in  1915  on  wheat;  since  then,  in  the  western  United 
States,  on  barley,  rye,  and  many  wild  grasses.  On  barley  it 
has  appeared  as  far  east  as  South  Dakota. 

Bunt,  Stinking-smut  ^-^  (Tilletia  Icevis  Kiihn,  Tilletia  tritici 
(Bjerk.)  Wint.).  —  Tilletia  tritici  causes  heavy  losses  in  the 
Northwest,  T.  Iwvis  in  the  eastern  United  States.  Where 
both  occur  the  first  is  known  as  ''low  smut,"  the  second  as 
"high  smut"  from  their  respective  habits.  This  smut  (for 
practical  purposes  the  two  may  be  considered  as  one)  is 
readily  distinguished  from  loose-smut  by  the  fact  that  it 
attacks  only  the  grain,  not  the  inclosing  chaff.  The  head 
therefore  remains  of  much  more  nearly  normal  appearance, 
and  it  is  often  not  until  the  glumes  have  been  opened,  and 
their  contents  examined,  that  the  presence  of  the  smut  mass  is 
detected,  covered  with  its  membrane,  and  resembling  the 
wheat  grain  in  size  and  shape.  It  may  be  recognized  by  an 
expert  observer  by  its  peculiar,  disagreeable,  penetrating 
odor,  and  by  the  deeper  green  color  of  the  diseased  heads. 
The  smut  masses  are  often  so  firm  as  to  remain  unbroken 
through  threshing,  but  they  may  be  recognized  among  the 
grains  by  their  darker  color,  greater  plumpness,  absence 
of  groove  and  germ,  and  finally  by  crushing  them  and  lib- 
erating the  black  spores. 

The  disease  is  particularly  destructive,  since  its  presence 
signifies  not  only  loss  of  grain  due  to  replacement  by  smut, 
but  also  loss  in  value  to  the  good  wheat,  which  may  be 
largely  depreciated  in  price  by  the  presence  of  the  bunt. 
Often  bunted  wheat  is  worthless  for  milling  purposes  and 
even  for  cattle  feed.  Bunt  constitutes,  for  these  reasons, 
one  of  the  worst  smuts  in  the  world.  Strong  fanning  re- 
moves part  of  the  smutted  grains,  but  troublesome  wash- 
ing processes  must  be  employed  to  remove  them  all.  and  even 
then  the  results  are  not  entirely  satisfactory.  The  annual 
loss  from  bunt  in  the  United  States  is  about  25,000,000  bu., 
to  which  should  be  added  the  frequent  loss  from  explosion 
of  threshing  machines,  estimated  at  $1,000,000  in  two  years, 
due  to  the  oily  combustible  spores.    Where  low  smut  alone  is 


Cereals  315 

present  and  the  heads  only  are  harvested,  the  sickle-bar 
may  be  so  adjusted  as  to  leave  the  bunt  behind. 

Many  smut  spores  naturally  find  lodgment  upon  the  sur- 
faces of  healthy  grains  from  smutted  fields,  or  they  may  be 
carried  from  farm  to  farm  upon  the  threshing  machine.  Upon 
planting  such  seed  the  following  season  these  spores  are 
ready  to  attack  the  seedling  grain  plant.  The  fungus,  after 
gaining  entrance  into  the  seedling,  grows  with  it  throughout 
the  season,  and  appears  again  at  harvest  time  as  spore  masses 
within  the  chaff.  Every  grain  of  every  head  of  an  affected 
plant  is  usually  snmtted. 

The  seedUng  age,  like  that  of  the  oat,  is  the  onh^  age  sus- 
ceptible to  smut  infection.  Treatment  of  seed  wheat  with 
formalin  is  usually  complete  in  its  efficiency  and  trifling  in 
cost.  In  some  sections  of  the  Northwest,  however,  the  soil 
has  become  so  heavily  infested  from  previous  cropping  and 
by  "smut  showers"  that  formalin  seed  treatment  is  of  but 
little  value.  In  such  regions  early  sowing  and  crop  rotation 
are  reconmiended. 

Loose-smut  ^-^  {Usiilago  tritici  (Pers.)  Rostr.).  — Like  the 
loose  smut  of  barley,  this  smut  seems  to  be  increasing  in 
importance.  In  some  regions  it  prevails  to  a  greater  ex- 
tent than  the  bunt,  causing  at  times  a  loss  of  more  than  a 
quarter  of  the  crop  though  the  loss  is  usually  not  more  than 
2  per  cent.  Loose-smut  may  readily  be  distinguished  from 
stinking-smut  of  wheat  by  the  fact  that  the  spore  masses 
involve  the  whole  spikelet,  which  becomes  dry  and  powdery 
and  falls  away;  also  by  its  much  earlier  appearance  in  the 
field,  i.  e.,  at  flowering  time.  The  spore  masses  are  dark, 
olive-black,  and  are  produced  exclusively  in  the  spikelets. 
The  bearded  spring  wheats  seem  to  be  more  susceptible 
than  the  blue-stem  varieties,  but  the  smut  is  common  on  all 
varieties. 

From  the  studies  of  Maddox  in  Tasmania,  Wakagwa  in 
Japan,  Brefeld  in  Germany,  and  othei's,  it  was  known  in  1896 
that  with  the  loose-smuts  of  wheat  and  barley,  totally  unlike 
the  bunt  of  wheat  and  the  loose-smut  of  oats,  infection 


316  Diseases  of  Economic  Plants 

occurs  exclusively  at  blossoming  time;  that  at  all  other 
times  the  plants  are  immune.  Smut  spores  from  near-by 
smutted  heads  are  blown  into  the  wheat  or  barley  flowers. 
Infection  follows.  The  fungus  then  lies  dormant  in  the 
grain  until  the  seed  sprouts.  If  the  grain  ripening  from 
such  infected  flowers  be  used  for  seed,  the  fungus  develops 
in  the  seedling,  and  an  infected  plant,  producing  smut  but 
no  grain,  results,  though  no  external  symptom  of  the  disease 
appears  until  blossoming  time.  Conversely,  if  seed  result- 
ing from  blossoms  which  were  not  infected  be  used,  plants 
free  from  smut  will  be  raised. 

The  remedy  in  this  case,  therefore,  lies  in  the  use  of  unin- 
fected seed.  To  obtain  such  seed,  grain  must  be  secured 
from  a  field  in  which  there  is  no  loose  smut,  or  if  this  is  not 
practicable,  seed  grain  must  be  raised  under  such  conditions 
as  will  afford  clean  seed. 

It  has  been  found  that  while  the  ordinary  formalin  seed- 
treatment  is  ineffective  against  wheat  loose-smut,  the  hot- 
water  treatment,  in  modified  form,  is  effective,  though  some- 
what difficult  of  manipulation.    See  p.  272. 

Rogueing  or  weeding  out  all  diseased  plants  from  the  crop 
that  is  to  be  used  for  seed,  diminishes  the  smut  largely,  but 
does  not  entirely  eliminate  it. 

A  practicable,  effective  means,  which  results  in  complete 
and  inexpensive  eradication  of  this  smut,  consists  of  a  com- 
bination of  the  seed  plat  with  the  hot-water  treatment. 

Flag-smut  ^^^'  ^^^  (Urocystis  tritici  Koern).  —  Linear,  black 
streaks  in  the  leaves,  much  like  those  shown  in  fig.  182, 
occur  on  wheat.  Considerable  damage  is  reported  from 
Australia,  India,  and  Japan.  Flag-smut  was  found  in 
Illinois  in  1919.  The  usual  formalin  treatment  is  beneficial, 
though  not  so  complete  in  control  as  with  oat  smut,  since 
infection  occurs,  to  some  extent,  from  diseased  refuse  in  the 
soil.  If  badly  infested,  the  stubble  should  be  burned  to 
destroy  as  many  spores  as  possible. 

Foot- rots. ''^^'  '"-'^^^'-''^  —  These  diseases  are  characterized  by  a 
brown  or  black-rot  on  the  lower  part  of  the  stem,  the  diseases 


Cereals  317 

occurring  in  the  fields  in  spots.  They  are  known  in  many 
countries  on  wheat,  oats,  barley,  rye,  and  rice,  and  are  very 
destructive  in  Europe  and  Australia.  The  diseases  in  their  va- 
rious forms  have  many  names,  among  them  Take-all,  White- 
heads, Pietin.  Any  one  of  several  fungi  may  cause  foot-rot, 
especially  when  the  wheat  plant  is  weakened  by  adverse  en- 
vironmental conditions.  A  foot-rot  of  wheat  due  to  unknown 
cause  was  reported  in  Oregon  in  1902,  and  one  due  to  Hel- 
minthosporium  in  Illinois  and  Indiana  in  1919.  Burning  of 
the  stubble  and  crop  rotation,  accompanied  by  good  drain- 
age, are  reconmiended. 

Anthracnose  {Colletotrichum  cereale  Manns).  —  This  an- 
thracnose  seems  to  prevail  on  wheat  as  extensively  as  upon 


Fig.  165.  —  Normal  wheat  kernels  and  shriveled  ker- 
nels due  to  anthracnose.    After  Manns. 

rye.  The  head  is  not  destroyed,  as  in  the  case  of  rye,  but 
general  weakness  of  the  plant  and  light,  shriveled  grain 
follows  the  attack. 

Powdery-mildew  ^^  (Enj.^iphe  (jraminis  DC).  —  The  usual 
characters  of  the  powdery-mildews  are  exhibited;  a  whitish, 
flour-like  coating  in  irregular,  circular  spots  upon  the  leaves 
and  other  plant  parts.  This  mildew,  together  with  the 
mildew  of  oats,  rye,  and  barley,  bears  the  same  specific 
name,  but  upon  each  of  these  crops  the  form  is  so  special- 
ized as  not  to  transfer  readily,  if  at  all,  to  the  other  crop 
plant.     Thus  from  the  farmer's  viewpoint  there  are  prac- 


318 


Diseases  of  Economic  Plants 


tically  four  distinct  kinds  of  mildew,  although  indistinguish- 
able to  the  eye.  The  form  upon  wheat  grows  upon  all  species 
of  Triticum  though  some  varieties  show  much  more  resistance 
than  others. 

In  damp,  shaded  spots  the  mildew  is  sometimes  quite 
injurious,  though  it  is  rarely  so  over  any  considerable  area. 

The  conditions  favor- 
ing the  disease  should 
be  avoided. 

Scab  '-'  (Gihherella 
sauhinetii  (Mont.)Sacc., 
Fusariwn) . —  Scab,  first 
described  in  1884  in 
England,  seems  to  be 
quite  generally  distrib- 
uted in  America,  and 
is  often  the  cause  of 
large  loss  which,  under 
conditions  favorable  to 
the  disease,  may  reach 
from  10  to  30  per  cent 
or  higher.  The  loss  in 
1917  was  estimated  as 
about  10,000,000  bush- 
els. Scab  appears  upon 
the  heads  when  about 
half  ripe,  as  yellow  or 
pink  incrustations  on 
the  spikelets,  on  the  bases  of  the  glumes,  or  covering  the 
rachis.  The  affected  spikelets  ripen  prematurely  and  turn 
yellow  or  brown  before  the  normal  parts  mature.  After 
ripening  of  the  head,  the  diseased  parts  appear  shrunken. 
The  grain  itself  is  shrunken,  covered  with  a  thick  felted 
mycelium,  and  is  incapable  of  germination. 

Only  a  few  spikelets  upon  the  head  may  be  affected,  these 
occupying  any  position  —  basal,  terminal,  or  intermediate 
—  or  the  whole  head  may  be  diseased.    The  loss  consists  in 


Fig.  166.  —  Anthnicnose  on  wheat  stems. 


Cereals  319 

injury  to  the  quality  of  the  grain  and  diminution  in  quan- 
tity. 

Selby  has  shown  that  seedHngs  in  the  field  are  often  killed 
by  this  disease,  which  is  carried  over  in  the  seed.  In  this 
way  as  high  as  5.9  per  cent  of  death  in  seedlings  has  been 
caused. 

It  has  recently  been  shown  that  the  fungus  that  causes 
wheat  scab  grows  also  on  corn  causing  root-rot,  and  winters 


b  a 

Fig.  167.  —  Wheat  kernels:  a,  normal;  b,  shrunken  and  killed  by 
scab.     After  Manns. 

on  corn  refuse.  Wheat  planted  in  fields  that  bore  infected 
corn  becomes  badly  diseased.  One  corrective  practice,  there- 
fore, is  to  avoid  sowing  wheat  on  land  so  infested. 

Minor  diseases 

Black-chaff  ^^^' ^"'^  (Pseudomonas  translucens) . — As  the 
wheat  approaches  maturity,  black,  sunken  stripes  appear 
lengthwise  of  the  chaff.  The  rachis  and  leaves  are  also  at- 
tacked. In  severe  cases  the  grain  is  shriveled.  The  disease 
was  found  in  15  states  west  of  Indiana  in  1917.  Thorough 
screening  and  disinfection  of  seed  by  copper  sulfate  is  ad- 
vised. Leptosphaeria  leaf-blight  ^^^  (Leptosphceria  tritici 
(Gar.)  Pass.).  —  The  lower  leaves  are  killed  early  in  the 
season.     Large   loss  is  not   usual.      The   Glume-blotch  ^''^ 


320  Diseases  of  Economic  Plants 

(Septoria  sps.)  is  common  as  small,  dark  spots  upon  the  chaff 
of  certain  varieties  of  wheat.  Another  Septoria  causes  leaf- 
spots,  especially  upon  the  lower  leaves.  Eel-worms  ^""^^  ^^'■^'  ^^'^ 
(Nematodes)  affecting  the  grain  in  the  head  have  been  found 
in  several  states,  in  some  fields  causing  25  per  cent  damage. 
Only  clean  seed  should  be  used.  Crop  rotation  is  advised. 
Ergot  is  occasional  on  wheat.  The  Southern-blight  (Sclero- 
tium)  sometimes  injures  the  stand  in  the  South. 


FORAGE  CROPS 

This  group  of  crops,  of  high  aggregate  value  and  agricul- 
tural necessity,  does  not  possess  an  acreage  value  which 
warrants  such  expensive  modes  of  treatment  as  spraying. 
Protection  against  disease  here  must,  in  general,  consist  in 
modifications  of  agronomic  methods  tending  to  produce 
thriftier,  more  resistant  plants,  crop  rotation  to  diminish  the 
parasites,  variation  of  time  of  sowing  or  harvesting  to  evade 
disease.  Forage  diseases  are  especially  troublesome  since 
they  frequently  prohibit  planting  of  certain  leguminous  crops 
much  desired  in  the  rotation. 

Legumes 
ALFALFA 

Leaf-spot  ^^^'  '*^^  (Pseudopeziza  medicaginis  (Lib.)  Sacc.) — 
No  other  disease  of  alfalfa  is  so  universally  prevalent.  It 
constitutes  the  most  important,  in  most  sections  the  only 
really  important,  disease  of  this  crop.  Loss  in  vigor  of  the 
plants  and  loss  in  hay,  by  shedding  of  the  leaves,  result. 
Pammel  in  Iowa  in  1891  estimated  the  loss  in  some  fields  at 
50  per  cent.  It  was  first  described  in  Europe  in  1832,  and 
noted  in  the  United  States  in  1875. 

The  leaves  first  show  small  brown  to  black  spots,  irregular 
or  circular,  which  extend  through  the  leaf  and  are  thus 
visible  from  both  sides.  They  are  about  1-2  mm.  in  di- 
ameter, and  are  not  sharply  bordered,  but  shade  off  grad- 
ually into  the  surrounding  tissue.  With  a  hand  lens  very 
small,  spore-bearing  organs  may  be  seen  in  the  centers  of 
the  older  spots,  first  as  shiny  amber-colored  elevations. 
These  elevations  soon  crack  open  and  expose  very  small, 
cup-shaped  sporiferous  bodies,  which  remain  surrounded  by 
portions  of  the  ruptured  epidermis.  Badly  diseased  leaves 
321 


322  Diseases  of  Economic  Plants 

usually  turn  yellow  and  fall  off.    Spots  upon  the  stems  show 
the  same  general  character  as  those  upon  the  leaves. 

The  lower  leaves,  and  the  leaves  of  older  plants,  are  most 
subject  to  the  leaf-spot.  Plants  late  in  the  season,  as  of 
the  second  and  third  cuttings,  suffer  much  more  than  earlier 
in  the  season.  These  crops,  especially  in  a  dry  season,  if 
allowed  to  stand  a  little  too  long  before  cutting  may  be  badly 
spotted,  and  the  loss  in  hay,  through  fallen  leaves,  may  be 


4^ 


1  L'  3  4 

Fig.  168.  — ■  Four  alfalfa  leaf-spots  due  to:  1,  Ascochyta;  2,  Pseudope- 
ziza;  3,  Cercospora;  4,  Stagonospora.    After  Stewart  and  others. 

considerable.  The  plants  are  never  killed  by  this  disease, 
though  young  fields  which  have  not  yet  become  well  estab- 
lished may  be  ruined. 

Its  mode  of  dissemination  is  unknown,  and  seed  treatment 
is  useless  as  a  preventive. 

The  only  practicable  treatment  is  to  mow  down  badly 
diseased  plants  with  the  hope  that  the  new  shoots  which 
spring  forth  may  overcome  the  disease.  If  the  disease 
appears  just  before  cutting  time,  the  mowing  should  be 
hastened  a  few  days  in  order  to  avoid  loss  from  leaf  shedding. 

Yellow  leaf-blotch  ^'"^  (Pyrenopeziza  medicaginis  Fcl., 
Sporonema).  —This  disease  is  known  from  Vermont  to  the 
Pacific,  in  Europe  and  South  America,  and  under  certain 


Forage  Crops  323 

conditions  does  more  damage  than  leaf-spot.  The  spot 
produced  is  deep  yellow,  verging  to  orange,  and  bears  nu- 
merous orange-colored  pycnidia.  The  fungus  winters  on 
infected  leaves.    Early  cutting  is  beneficial. 

Wilt  ^"'^  {Sclerofinia  trifoUorum  Eriks.).  —  This  wilt,  which 
in  some  respects  resembles  lettuce  drop,  has  been  noted  on 
alfalfa  and  the  clovers,  red,  white,  crimson,  bastard,  mam- 
moth, and  alsike,  in  several  widely  separated  sections  of  the 
United  States  and  Europe. 

It  kills  the  plants,  and  under  favorable  weather  conditions, 
the  chief  factor  of  which  is  a  humid  atmosphere,  it  may  ex- 
tend from  plant  to  plant  and  involve  large  areas  in  the  field. 

Plants  may  show  a  variety  of  symptoms.  Sometimes  the 
leaves  droop,  and  become  matted  together  in  a  sodden  mass 
at  the  base  of  the  plant,  and  overgrown  with  a  white  cotton- 
like layer  of  mycelium,  in  which  black  sclerotia,  similar  to 
those  described  under  lettuce,  are  found.  At  other  times  the 
stems  may  be  the  point  of  attack,  showing  dead,  brown  sec- 
tions covered  with  the  mycelium  and  bearing  sclerotia. 
Upon  splitting  a  stem  open  the  central  part  may  be  found 
filled  with  mj^celium  and  with  occasional  sclerotia  about  the 
size  of  a  grain  of  wheat.  The  white  mycelium  and  black 
sclerotia  are  absolutely  diagnostic. 

Under  unfavorable  weather  conditions  the  disease  may 
die  out  and  fail  to  reappear,  but  if  the  weather  is  favorable 
to  this  fungus,  the  wilt  may  reappear  year  after  year  with 
increased  severity,  involving  larger  and  larger  areas. 

Stewart,  French,  and  Wilson  reported  large  areas  where 
50  per  cent  of  the  stalks  were  killed,  though  later  the  field 
recovered  entirely. 

Where  the  disease  is  troublesome,  rotation  of  crops  and 
deep  plowing  to  bury  the  sclerotia  seem  to  be  the  only  re- 
course. Isolated,  infested  areas  may  be  cleaned  out  by  burn- 
ing. 

Texas  root-rot  ^^'^^  (Ozonium).  —  This  rot  is  a  soil  disease, 
which  in  its  general  characters  is  identical  with  that  so 
disastrous  upon  cotton  and  the  treatment  applied  to  cotton 


324 


Diseases  of  Economic  Plants 


is  the  only  one  to  be  recommended  for  alfalfa.     It  has  been 
very  destructive  in  Texas  since  1892. 

Anthracnose  ^''•*    {Colletotrichum    trifolii    Bain).  —  Alfalfa 
anthracnose  was  first  mentioned  in  1905  l^y  Bain  and  Essary, 

who  stated  that  it  was  prev- 
alent in  Tennessee  in  1906 
and  was  one  of  the  chief 
causes  of  alfalfa  failures  in 
that  state.  It  has  also  been 
noted  in  destructive  form 
in  Virginia  and  New  York. 
It  appears  as  elliptical, 
sunken  spots,  5-6  mm. 
long,  upon  the  stems.  The 
spots  are  gray  and  have 
dark  acervuli  scattered 
over  them.  Where  the 
disease  l)ecomes  aggressive, 
dead  or  withered  stalks  or 
plants  are  seen  scattered 
over  the  field.  These  stalks 
arise  from  diseased  crowns, 
which  are  characterized  by 
blackening  of  the  woody 
parts,  below  the  point 
where  the  stalks  are  at- 
tacked. The  only  remedy 
seems  to  be  the  use  of  re- 
sistant varieties. 

Blight  ^"'  ''^  (Pseudomo- 
nas  medicaginis  Sack.).  — 
From  Colorado  Paddock, 
in  1906,  described  a  severe 
disease  of  alfalfa  which  has 
been  noted  for  several  successive  years.  It  is  due  to  bac- 
teria and  in  its  early  stages  produces  a  watery,  semi- 
transparent,  yellowish  to  olive-green  appearance  along  one 


Fig.  169.  —  Alfalfa  crown-wart. 
After  U.  S.  Department  of  Agri- 
culture. 


Forage  Crops  325 

side  of  the  stem  of  the  plant.  The  plants  are  at  first 
weak,  the  stems  light  colored,  later  discolored  or  black- 
ened. Drops  of  thick  fluid  exude  from  the  stems  and  dry 
upon  them,  giving  a  glistening  appearance  as  if  they  were 
varnished.  The  chief  damage  is  to  the  first  cutting,  though 
in  subsequent  years  the  plants  may  die  from  decay  of  the 
crown,  or  roots,  or  from  loss  of  nutrition.  Infection  takes 
place  chiefly  through  rifts  in  the  epidermis  due  to  frost, 
thereby  affording  access  to  wind-borne  bacteria. 

Crown- wart  ^^'^  (Urophlydis  alfalfce  (Lag.)  Magn.). — 
The  chief  diagnostic  character  is  the  presence  of  numerous 
galls  at  or  near  the  base  of  the  stem.  They  vary  greatly  in 
size  from  that  of  a  pea  to  an  orange.  Diseased  plants  have 
brown,  dead  stems,  or  stems  that  are  weak  and  bear  yellow 
leaves.  The  disease  apparently  originated  in  South  America, 
is  now  widely  distributed  in  Europe  and  was  first  noted  in  the 
United  States,  in  California,  in  1909,  later  in  Arizona,  Oregon, 
and  Utah. 

Dodder  ^^^  (Cuscuta  sps.).  —  Dodder,  or  love  vine,  is  a 
parasitic,  flowering  plant.  Its  yellow,  threadlike  stems  coil 
closely  around  the  alfalfa  stems,  and  take  nourishment  from 
them.  It  reproduces  by  seed,  and  the  seed  may  readily  pass 
with  alfalfa  seed  unless  very  carefully  inspected.  The 
parasite  is  absolutely  ruinous  to  the  portions  of  the  field 
that  it  infests  and,  since  it  spreads  rapidly,  it  is  a  serious 
enemy. 

If  dodder  occurs  in  spots,  these  should  be  dug  over  or 
burned  over  before  it  ripens  its  seed,  using  kerosene  and 
straw  to  insure  heat  suflEicient  to  kill  every  plant,  with  a 
margin  of  a  few  feet  entirely  around  the  infested  spot. 
Badly  infested  fields  should  be  plowed  up. 

Minor  diseases 

Root-rot,  wilt  {Fusarium  sp.).  —  The  first  symptom  of 
this  wilt  is  a  yellowing  of  the  outer  leaves  which  gradually 
spreads  until  all  of  the  leaves  and  stems  become  discolored, 
wilt,  and  die.    This  rot  is  said  to  be  quite  generally  destruc- 


1  2  3 

Fig.  170.  —  1,  Alfalfa  seed;  2,  seed  of  large- 
seeded  dodder;  3,  seed  of  small-seeded  dodder, 
natural  size.    After  Stewart  and  others. 


Fig.  171.  —  Alfalfa  plant  and  dodder.   After  Stevrart 
and  others. 


Forage  Crops  327 

tive  in  Arizona.  It  is  a  soil  disease,  and  its  general  characters 
are  those  indicated  on  p.  26. 

Root-rot  {Rhizoctonia  crocoriim  DC). — Similar  to  the 
effects  of  Rhizoctonia  upon  so  many  other  hosts,  the  disease 
consists  primarily  of  a  root-rot  in  which  the  diseased  parts 
are  coated  with  matted  strands  of  the  fungous  mycelium, 
usually  brownish  red  or  violet  in  color,  accompanied  by 
sclerotia.    The  tops  of  plants  so  diseased  turn  yellow  and  die. 

The  very  aggressive  fungus  migrates  through  or  over  the 
soil  to  adjoining  plants,  and  the  affected  spot  in  the  field 
thus  enlarges,  sometimes  at  a  rate  of  7  m.  radially  per  year. 
Though  long  known  in  Europe,  it  has  not  yet  appeared  in 
many  parts  of  America. 

Rhizoctonia  root-rot  is  a  typical  soil  disease  and  is  kept 
alive  in  the  soil  by  its  sclerotia,  which  may  live  at  least  two  or 
three  years.  The  general  suggestions  given  under  soil  dis- 
eases apply. 

Ascochyta  leaf-spot  (Ascochyta  medicaginis  Bres.).  — This 
leaf-spot  has  been  noted  in  North  Carolina,  and  what  is 
probably  the  same  disease,  also  in  New  York.  The  spots  are 
irregularly  circular  except  where  they  occur  on  the  edge  of 
the  leaf,  light  brown  in  color,  and  bear  small  black  dots. 

Cercospora  leaf-spot  (Cercospora  jnedicaginis  E.  &  E.), 
which  appeared  in  Delaware  in  1889,  has  also  been  noted  in 
New  York  and  New  Jersey.  The  leaf-spots  are  nearly  circu- 
lai',  smoky  brown  to  black,  from  0.5-1  mm.  in  diameter,  and 
show  equally  well  from  either  surface  of  the  leaf.  They  have 
no  well-defined  borders,  but  shade  into  the  surrounding 
healthy  tissue.  Affected  leaves  turn  yellow  and  die.  It  ap- 
pears to  be  disseminated  on  the  seed.  Seed  disinfection  is 
therefore  recommended.  A  leaf-spot  has  also  been  described 
due  to  Pleosphcerulina  hriosiana  Poll.,  and  others  due  to 
Septoria  and  Macrosporium. 

Downy-mildew  (Peronosporn  frifoUorum  De  Bary)  is  a 
serious  pest  on  clover  in  Ein'ope  and  has  been  reported  in 
America  from  Colorado,  Kansas,  New  York,  and  North 
Carolina,  though  it  has  not  yet  been  destructive  in  this 


328  Diseases  of  Economic  Plants 

country.  The  affected  parts  of  the  leaf  turn  yellowish  gray  to 
purple,  and  are  frequently  curled.  The  leaves,  as  seen  from 
below,  are  coated  with  a  downy  fuzz,  violet  colored  when  old. 

Rust  (Uromyces  striatus  Schr.)  may  be  recognized  by  the 
typical  rust  sori,  which  are  present,  in  this  case,  chiefly  upon 
the  lower  sides  of  the  leaves.  The  cluster-cup  stage  is  found 
on  Euphorbia.  Anthracnose  (Gloeosporium  medicagitiis  E.  & 
K.).  —  Black,  rather  prominent  acervuli  appear  chiefly  upon 
the  lower  surfaces  of  leaf-spots.  The  lower  leaves  often 
turn  yellow  and  die.  Seed-mold  {AUernaria  sp.).  —  Brown, 
dead,  shriveled  seeds  are  often  noted  in  samples  of  alfalfa 
seed.  Such  seeds,  if  planted,  develop,  apparently  from 
within,  a  dense  black  mold. 

Damping-ofif  (Rhizoctonia  sp.  and  Pythium  deharyanwn 
Hesse)  is  caused  chiefly  by  the  two  fungi  named.  It  has 
been  known  to  affect  alfalfa  seedlings  in  the  greenhouse, 
and  it  may  occur  to  some  extent  in  the  field,  especially  the 
form  caused  ])y  Rhizoctonia. 

Stagonospora  leaf-spot  (Stagonospora  carpathica  Baeu.) 
has  been  noted  only  in  New  York.  Stewart,  French  and 
Wilson  characterize  this  leaf-spot  as  follows:  Unlike  the 
Ascochyta  leaf-spot,  this  disease  attacks  chiefly  green  leaves 
in  the  upper  part  of  the  plant.  The  spots  are  circular, 
1-3  mm.  in  diameter,  and  usually  light  brown  with  a  narrow 
border  of  dark  brown.  Each  spot  bears  several  light  brown 
pycnidia  visible  on  both  surfaces  of  the  leaf.  Yellow-top 
may  appear  simultaneously  over  whole  fields.  The  cause  is 
unknown.  White-spot  is  common  but  also  is  of  unknown 
cause. 

CLOVER 

Black-mold  (Phyllachora  trifolii  (Pers.)  Fcl.,  Polythrin- 
cium).  —  Common  red  clover,  crimson  clover,  white  clover, 
alsike  clover,  and  several  other  related  plants  are  affected  by 
this  mold.  The  chief  symptoms  are  pale  spots  upon  the  upper 
sides  of  the  leaves  accompanied  by  Ijlack  dots  on  the  lower 
sides.    These  spots  at  first  glance  so  strongly  resemble  the 


Forage  Crops 


329 


sori  of  the  rusts  as  to  lead  the  casual  observer  to  mistake  the 
disease  for  a  rust.  Though  the  disease  is  often  of  considerable 
damage,  no  treatment  is  known. 

Wilt  ^^'^  {Sclerotinia  trifoUorum.  Eriks.).  —  The  fungus  caus- 
ing this  wilt  is  probably  identical  with  that  of  the  wilt  of 
alfalfa.  It  was  first  noted  in  America,  in  Delaware,  by 
Chester  in  1889,  later  in  New  Jersey  by  Halsted. 

The  affected  plants  wilt  and  rot  to  the  ground.  White 
mats  of  mycelial  threads,  and  later  black  sclerotia,  are 
found  upon  or  within 
the  dead  stems.  Scle- 
rotia are  especially 
abundant  at  the  bases 
of  diseased  stems. 
Disk-like  bodies,  simi- 
lar to  those  described 
in  connection  with 
lettuce  drop,  develop 
from  the  sclerotium 
and  bear  spores  which 
spread  the  infection. 
While  this  malady  has 

been  very  destructive  in  Europe  upon  several  varieties  of 
clover,  it  is  not  yet  of  wide  distribution  in  America,  though 
it  has  appeared  as  a  serious  pest  in  a  few  fields. 

It  is  exceedingly  difficult  to  eradicate  when  it  has  once 
gained  foothold,  and  the  European  recommendation  is  to 
avoid  planting  the  infested  fields  to  susceptible  crops. 

Rust  {Uromyces  sps.). — The  clover  rusts  are  most  in- 
jurious to  the  second  cutting,  to  which  they  may  cause  a 
damage  of  20  or  even  50  per  cent  if  conditions  favorable  to  the 
disease  —  damp,  cool  weather  —  obtain.  These  rusts,  long 
known  in  Europe,  were  first  reported  in  America  in  1884.  At 
the  present  time  they  are  found  upon  red,  white,  crimson,  and 
alsike  clovers  over  a  large  part  of  the  United  States,  though 
of  different  species,  or  at  least  different  biologic  races  upon 
some  of  the  different  hosts. 


Fig.  172.  — ■  Clover  leaf  showing  spots  of 
black-mold.    Original. 


330 


Diseases  of  Economic  Plants 


These  are  true  rusts,  and  on  the  white  clover  possess  all 
of  the  three  stages,  cluster-cup,  summer  or  ureclinial,  and 
winter  or  teliospores.  They  attack  all  green  parts  of  the 
plant.  The  most  conspicuous  and  destructive  stage  is  the 
uredinial,  which  is  marked  loy  profuse,  circular  or  elongated, 
chestnut-brown,  powdery  sori.  These  may  be  few  and 
scattered,  ])ut  more  often  they  are  abundant,  nearly  covering 
the  leaf,  which  turns  black,  dies,  and  shrivels.  The  rust  is 
conveyed  from  plant  to  plant  throughout  the  summer  by 
spores  of  this  stage. 

The  teliospores  or  urediniospores  may  appear  in  the  same 
or  separate  sori  and  in  either  event  the  teliospores  appear 
later  in  the  season.  They  are  rec- 
ognized by  their  darker  brown 
color.  The  cluster-cup  stage,  which 
is  less  abundant  and  less  injurious 
than  the  other  stages,  may  often 
pass  unnoticed.  It  appears  first  as 
pale,  swollen  regions  upon  the  leaf 
or  petiole.  These  regions  soon 
show  the  characteristic  cups  with 

I  orange-colored  spores.   The  cluster- 

cup  stage,  though  not  known  on 
red  clover,  predominates  in  the 
early  spring  upon  many  other 
varieties;  but  the  uredinial  stage 
soon  gains  the  ascendancy  over  it. 
All  three  forms  may  be  produced 
side  by  side,  to  some  extent, 
throughout  the  summer.  Hiber- 
nation probably  occurs  in  two 
ways,  by  the  teliospores  and  by  the 
mycelium,  which  may  remain  alive 
in  the  affected  parts  over  winter. 
Anthracnose '^'^^^  {Colletotrichum  triJoUi  Bain).  —  This  an- 
thracnose  is  now  known  on  clovers  and  alfalfa  in  Tennessee, 
Ohio,  West  Virginia,  Arkansas,  Kentucky,  and  Delaware. 


Fig.  173.  —  Antliracnose 
on  red  clover  stem  and 
petiole.    After  Jackson. 


Forage  Crops  331 

It  is  first  found  chiefly  upon  the  leaf  stalks,  later  upon  the 
stems,  near  the  surface  of  the  ground  and  just  below  the 
flower  clusters,  as  elongated  sunken  spots,  which  result 
eventually  in  the  cleath  of  the  whole  plant.  It  frequently 
causes  great  loss,  and  is  said,  by  Bain,  to  be  the  most  serious 
plant  disease  in  Tennessee.  Alsike  clover  is  nearly  immune. 
Hope  lies  in  the  use  of  resistant  varieties. 

Anthracnose  {Glceosporium  caulivorum  Kirch.).  —  Long, 
brown  to  black,  sunken  spots  upon  stems  and  petioles,  caus- 
ing death  of  the  more  distal  parts,  are  diagnostic  characters 
of  this  anthracnose,  which  was  first  reported  in  the  United 
States  by  Sheldon  in  1906,  and  has  since  been  noted  as 
serious  in  a  number  of  states. 

Minor  rliseases 

Leaf-spot  ^-^  {Pseudopeziza  trifolii  (Biv-Bernh.)  Fcl.). — 
This  leaf-spot  much  like  that  of  alfalfa  occasionally  causes 
considerable  damage.  A  Cercospora  leaf-spot  is  also  re- 
corded. Black-mold  {Macrosporium  sarcinceforme  Cav.)  is 
widely  distributed  as  the  cause  of  concentric  spots  on  leaf 
and  petiole.  Scab  (GibbereUa  saubinetii,  Fusarium) .  —  This 
parasite  of  cereals  is  also  known  to  cause  depressed,  oblong 
spots  upon  clover.  See  wheat.  Broom-rape  (Orobanche 
minor  L.)  is  similar  to  that  upon  tobacco.  See  p.  259.  Root- 
rot  (Rhizodonia)  is  sometimes  injurious.  Dodder.  See 
alfalfa. 

COWPEA 

Wilt  ^•^'^  (Fusarium  vasinfectum  Atk.).  —  This  disease, 
closeh^  like  wilt  of  cotton,  okra,  and  watermelon,  is  not  com- 
municable from  one  of  these  plants  to  the  other,  though  it  is 
identical  with  the  wilt  of  the  soy  bean. 

It  first  appears  when  the  plants  are  about  six  weeks  old. 
Up  to  this  time  they  grow  well  and  appear  healthy.  Scat- 
tered plants  then  begin  to  drop  their  leaves,  the  lower  ones 
falling  first.    Growth  is  checked,  and  the  stem  shows  a  faint 


332 


Diseases  of  Economic  Plants 


reddish  brown  tinge.  After  the  leaves  have  fallen  the  stem 
dies  and  becomes  covered  with  a  light  pink  coating  of  the 
spores  of  the  wilt  fungus.  The  spread  of  the  disease  is  more 
gradual  and  less  conspicuous  in  the  early  part  of  the  season, 
but  after  the  peas  begin  to  set  fruit  they  succumb  rapidly,  and 

a  field  that  in  July  gave 
promise  of  a  fine  crop  may  be 
entirely  dead  before  Septem- 
ber without  having  matured 
a  pod.  The  disease  usually 
appears  in  spots,  like  the 
VN\  11    \       if    Yf^— ^  cotton  wilt,  and  these   dis- 

^/^^^j  \      //^^^         eased  areas  may  spread  until 

a  whole  field  is  involved. 

In  moderate  cases,  or 
where  the  varieties  planted 
are  less  subject  to  disease, 
only  the  weaker  plants  are 
killed,  while  the  rest  are 
dwarfed  and  their  yield  re- 
duced. Careful  examination 
of  the  roots  shows  that  many 
of  the  small,  lateral  roots  are 
dead,  small  tufts  of  roots 
marking  the  points  of  infec- 
tion (Fig.  174).  This  tufting 
of  the  rootlets  is  similar  to 
that  produced  on  cotton  by 
the  cotton-wilt  fungus. 
In  all  cases  the  veins  of  the  stem  are  brown,  and  the  dis- 
ease may  clearly  be  distinguished  by  cutting  across  the  stem 
to  observe  whether  the  color  of  the  wood  is  normal.  This 
discoloration,  which  may  often  be  seen  through  the  translu- 
cent stem  of  the  cowpea,  is  characteristic  of  this  class  of 
diseases.  The  name  "wilt"  is  somewhat  misleading,  since 
the  leaves  usually  drop  off  before  there  is  any  conspicuous 
wilting. 


Fig.  174.  —  Roots  of  diseased  cow- 
pea  at  left;  healthy  roots  on  the 
right.    After  Orton. 


Forage  Crops 


333 


334 


Diseases  of  Economic  Plants 


The  causal  fungus  is  spread  by  the  ways  suggested 
under  soil  diseases.  The  disease  is  now  known  in  most 
of  the  Southern  States  from  North  Carolina  to  Florida, 
and  west  to  Texas,  and  is  yearly  noted  in  new  lo- 
calities. 


Fig.   176.  —  Nematode  galls  on  roots  of  Unknown  cowpea.     After 
Lewis. 


Owing  to  the  all-important  position  the  cowpea  occupies 
in  southern  agriculture  as  a  nitrogen  crop,  where  the  best 
rotation  demands  its  frequent  recurrence  upon  the  same 
soil,  the  disease  is  of  peculiar  moment. 

No  remedy  is  known  except  the  use  of  the  Iron  cowpea  or 


Forage  Crops 


335 


its  derivatives,  the  resistance  of  which  was  noted  by  WilHams 
of  South  CaroUna  in  1900. 

Root-knot   (nematodes)  is  especially  destructive  on  cow- 
peas.     The  Iron  or  Brabham  varieties  are  resistant. 


Fig.  177.  —  Roots  of  the  Iron  cowpea  free  from  nema- 
tode galls.    After  Lewis. 


Minor  diseases 

Leaf-spot  {Amerosporium  oeconomicum  E.  &  T.).  —  This 
disease  is  readily  distinguished  from  the  angular  leaf-spot  in 
that  the  spots  are  circular,  are  of  shiny  whiteness,  and  are 
studded  all  over  with  black  pycnidia,  smaller  than  a  pinhole 
(Fig.  178).  The  disease  is  often  abundant,  but  is  usually  not 
so  serious  as  the  angular  leaf-spot. 


Fig.  179.  —  Cowpea  leaflet  spotted 
with  powdery-mildew.     Original. 


Fig.  180.  — ■  Leaflet  of  cowpea  showing 
Cercospora  spots.    Original. 


Forage  Crops  337 

Powdery-mildew  (Erijsiphe  polijgoni  DC).  —  The  white 
spots  of  this  mildew  are  strictly  circular  when  j^oung,  but 
as  they  enlarge  they  coalesce  and  cover  the  whole  upper 
surface  of  the  leaves  with  a  white  powder. 

The  disease  is  very  widespread,  but  even  in  the  worst 
seasons  does  not  do  much  injury. 

Angular  leaf-spot  (Cercospora  cruenta  Sacc). — ^  The  an- 
gular leaf-spots  of  this  disease  are  a  familiar  sight  in  most 
cowpea  fields.  They  are  of  various  colors  above,  chiefly 
reddish,  and  are  gray  to  purplish  or  slate-colored  below. 
The  damage  is  rarely  very  great.  In  some  instances  the  at- 
tack may  proceed  to  the  stems,  where,  especially  at  the  base, 
it  may  cause  cracking  and  result  in  such  lowering  of  the  vigor 
of  the  plant  as  to  cause  shedding  of  leaves  and  failure  to 
properly  fill  the  pods.  The  loss  of  leaves  is  of  course  serious 
to  the  hay  value  of  the  crop. 

Root-rot  (Thielavia);  a  Phyllosticta  leaf-spot  and  a  Sep- 
toria  leaf-spot  also  occur.    Streak.     See  sweet  pea. 

JAPAN  CLOVER  (Lespedeza) 

Powdery-mildew  {Microsphcem  diffusa  C.  &  Pk.).  — 
The  usual  characters  of  the  powdery-mildews  distinguish 
this  disease  sufficiently.  The  injury  to  this  valuable  southern 
forage  plant,  while  considerable,  is  never  sufficient  to  call 
for  treatment. 

SOY   BEAN   (Soja) 

Bacterial  blight  •'32-534  (Pseudnmonas  glycineum  Coerper) .  — 
Small,  angular  spots,  1-2  mm.  in  diameter,  at  first  water 
soaked,  translucent,  later  yellow  or  brown  and  eventually 
brown  or  purplish  black,  occur  on  the  leaves  and  pods 
accompanied  by  a  bacterial  exudate. 

The  disease  has  been  reported  from  Nebraska,  Connecti- 
cut, Wisconsin,  and  North  Carolina. 

It  is  thought  to  be  seed-borne. 

Wilt.    See  cowpea. 


338  Diseases  of  Economic  Plants 

VETCH 

Spot  {Protocoronos'pora  nigricans  A.  &  E.).  —  Upon  the 
stems,  leaves,  and  bracts  of  vetch  very  characteristic,  long, 
narrow,  or  elliptical  spots  are  formed,  frequently  with  a  dull 
purple  border,  and  usually  with  a  white  center.  When  on 
the  pods,  they  are  obliquely  situated.  When  old,  they  ap- 
pear as  black,  oblique  lines.  No  serious  damage  has  been 
reported. 

Downy-mildew  {Peronospora  vicioe  (Berk.)  De  Bary); 
Powdery-mildew  {Erysiphe);  Rust  {Uromyces  sps.),  and 
Leaf-spot  {Mycosphcerella)  see  pea,  are  of  minor  importance. 

Grasses 

Many  of  the  diseases  listed  below  on  special  grasses  should 
perhaps  be  considered  as  general  grass  diseases.  Thus  the 
smut,  Ustilago  striceformis,  is  known  on  many  genera  of 
grasses.  Grasses  in  general  are  susceptible  to  powdery- 
mildew,  Phyllachora,  Ergot,  and  rust.  The  biologic  rela- 
tionships of  but  few  of  these  have  as  yet  been  studied  on 
account  of  their  comparatively  small  economic  significance. 

BARNYARD -GRASS  (Panicuni) 

Smut  (Ustilago  crusgalli  T.  &  E.)  is  common  and  is  i-eadily 
recognized  by  the  usual  smut  characters.  No  treatment  is 
recommended. 

BLUEGRASS  (Poa) 

Rust  (Puccinia  poaruni  Niels.).  —  The  uredinia  of  this 
rust  take  even  greater  prominence  than  do  the  uredinia  of 
other  rusts;  indeed  other  forms  of  spores  are  almost  entirely 
absent  in  most  parts  of  the  country,  throwing  the  burden  of 
perpetuation  of  the  species  entirely  upon  the  uredinial 
mycelium  and  its  spores.  This  stage  is  known  to  be  peren- 
nial as  far  north  as  Washington,  D.  C.,  Nebraska,  and  Min- 
nesota.   The  secia  occur  on  Tussilago. 


Forage  Crops  339 

The  rust  is  destructive,  but  seems  to  be  limited  to  this  one 
host. 

Smut.    See  timothy. 

Anthracnose.    See  rye. 

Minor  diseases  are  caused  by  Uromyces  pace  Rab.,  Phyl- 
lachora  poce  (Fcl.)  Sacc,  and  Ergot. 

CRABGRASS 

Blast  {Piricularia  oryzce  Cav.).  —  This  is  probably  iden- 
tical with  rice  blast.     See  p.  300. 

JOHNSON  GRASS.     See  sorghum,  p,  307,  which  has  similar 
diseases. 

MILLET.     See  p.  295. 

ORCHARD -GRASS  (Dactylis) 

Leaf-spot  {Scolecotrichum  graminis  Fcl.).  —  Elliptical, 
dead  spots  may  appear  upon  orchard-grass  and  on  several 
other  grasses,  conspicuous  upon  the  lower  outer  leaves. 
Death  of  the  leaf  follows  sometimes,  starting  at  the  leaf  tips 
and  reaching  to  the  base.  In  conditions  favorable  to  the 
disease  whole  plants  are  involved.  The  spots,  before  they 
become  confluent,  are  of  quite  characteristic  appearance: 
large,  dark  brown  to  purplish  brown.  When  old,  they  usually 
show  at  their  centers  spots  of  gray  or  white,  and  these  spots 
may  be  marked  with  small,  black  specks  arranged  in  rows 
lengthwise  of  the  leaf. 

Black-stem-rust  (Puccinia  graminis  Pers.).  —  This  rust 
fungus  may  be  either  of  the  oat,  orchard-grass,  or  Agrostis 
strain. 

Crown-Rust  {Puccinia  coronata  Cda.).  —  See  oats,  p.  298. 

Anthracnose.    See  rye,  p.  307. 

Rathay's  disease  {Bacterium  rathayi  (EFS.) )  ^''^  develops 
'with  thick  layers  of  bacteria  on  the  surface  of  the  plant, 
causing  an  unusual  type  of  plant  disease. 


340 


Diseases  of  Economic  Plants 


PASPALUM 

Ergot  '^^^  {Claviceps  paspali  S.  &  H.  and  C.  rolfsii  S.  &  H.). 
—  The  ergots  displacing  the  grain  are  somewhat  smaller  than 
a  pea,  irregularly  globular  in  outline,  and  pale  yellow  in 

color.      Stock       poisoning 

from  pasturing  on  grass 
bearing  these  ergots  is  com- 
mon in  the  South.  Mow- 
ing the  green  heads  before 
the  ergot  develops  will  les- 
sen the  danger. 

QUACKGRASS  (Agropyron) 
Smut  ( Urocystis  agropyri 
(Preuss.)  Schroet  and  Usti- 
lago) .  —  These  smuts  re- 
semble each  other  in  the 
general  appearance  of  the 
sori,  though  microscopi- 
cally the  characters  are 
quite  different. 

REDTOP  {Agrostis) 

Black-stem- rust  {Puccinia  graminis  agrostis  Erks.).  — 
The  rust  is  identical  with  that  upon  wheat  and  oats,  though 
infection  does  not  readily  pass  from  one  host  to  the  other. 

Smut  (Ustilago  striceformis  (West.)  Niessl).  —  This  is 
the  smut  described  under  timothy.  It  has  been  known 
to  affect  30  per  cent  of  the  plants,  and  to  reduce  the  seed 
yield  from  300  hundredweight  to  70  hundredweight. 

Anthracnose.    See  rye. 


Fig.  181.  —  Ergot  on  Paspalum. 
After  Beal. 


TALL  OATGRASS 

Smut  {Ustilago  perefinans  Rostr.).  —  This  smut  closely 
resembles  that  of  oats,  though  the  flower  parts  are  not  so 
completely  destroyed  as  in  oat  smut.    The  disease  is  peren- 


Forage  Crops 


341 


nial  in  its  perennial  host,  and  smutted  plants  bear  smut, 
year  after  year. 


TIMOTHY  (Phleum) 

Smut  ^^^  (Ustilayo  stricefornus  (West.)  Niessl).  —  This  smut 
occurs  chiefly  upon  the  leaves,  more  rarely  upon  other  parts 
of  timothy,  as  well  as 
upon  many  species  of 
Agrostis,  Poa,  Elymus, 
Bromus,  Dactylis,  Fes- 
tuca,  in  Europe,  Australia, 
and  generally  throughout 
the  United  States.  The 
spore  masses  form  long 
black  lines  upon  the  leaf, 
and  by  merging  and  rup- 
turing reduce  the  leaf  to 
a  torn,  blackened  state. 
The  affected  plants  are 
small,  weak,  and  often  fail 
to  make  seed  and  the  hay 
value  is  thus  lowered. 
The  disease  is  perennial 
within  the  host.  Infec- 
tion takes  place  in  the 
blossom,  resulting  in  a 
seed  bearing  the  myce- 
lium of  the  smut.  Hot- 
water  treatment  of  seed 
(cold  water  6  hours,  52° 
C.  (123°  F.)  15  minutes) 
gives  promise  of  success. 

Rust  ^^^  (Puccinia  grani- 

inis     phleipratensis) .  —  „      ,„       o    •    /-tt.-, 

rp,-            .    •                   1  Fig.  182.  —  Son  of  Ustilago  strisefor- 

This   rust   m   general   re-  „,i,  j^  leaves  of  timothy.    After 

sembles  the  black-rust  of  Osner. 


342  Diseases  of  Economic  Plants 

the  grains.  It  was  first  reported  in  1882  and  has  of  recent 
years  increased  rapidly.  It  can  be  transferred  easily  to 
various  grasses.  The  secial  host  is  not  definitely  known, 
but  probably  is  not  the  barberry.  The  rust  winters  mainly 
in  the  uredinial  stage. 

A  Stripe-blight  (bacteria)  is  recorded. 

Powdery-mildew  is  common  but  not  serious. 

Anthracnose.    See  rye. 


FIBER  PLANTS 
COTTON  3^5 

-^^1^369  (Fusariu?n  vasinfectum  Atk.).  —  The  cotton  wilt, 
now  widely  distributed  and  yearly  preempting  more  territory, 
is  caused  by  a  fungus  that  plugs  the  water  ducts  in  the  veins 
of  the  stem  and  cuts  off  the  water  supply  to  the  parts  above, 
always  reducing  the  vigor  of  the  plants  and  usually  resulting 
in  speedy  death. 

Soil  which  produces  a  diseased  crop  one  year  is  so  infested 
with  the  causal  fungus  as  to  insure  its  reappearance  in  more 
extensive  areas  in  subsequent  croppings.  The  destructive- 
ness  of  a  disease,  which  takes  not  only  the  crop,  but  in  part 
the  usefulness  of  the  soil  as  well,  cannot  be  estimated.  Its 
injury  can  only  be  realized  by  those  who  have  experienced  its 
effects. 

Wilt  has  long  been  known  by  Southern  cotton  planters, 
both  on  cotton  and  okra,  and  is  now  prevalent  in  many  sec- 
tions of  Alabama,  Arkansas,  North  Carolina,  South  Carolina, 
Georgia,  Louisiana,  and  probably  throughout  the  whole 
cotton  belt.  Many  foreign  countries  also  record  it.  Loss  in 
Georgia  was  estimated  as  SI, 000,000  annually,  prior  to  the 
use  of  resistant  varieties. 

The  first  indication  of  wilt  appears  as  a  yellowing  of  the 
lower  leaves  at  the  edges  or  between  the  main  ribs,  which 
portions  may  become  almost  white;  later  they  turn  brown 
and  die.  A  single  leaf  often  presents  the  three  conditions, 
green  (healthy),  yellow  (sick),  and  brown  (dead),  in  bands 
side  by  side,  parallel  to  the  main  ribs  and  radiating  from 
the  leaf  stem.  The  dead  parts  may  break  away,  leaving  the 
leaf  ragged.  The  upper  leaves  rapidly  follow  the  course  of  the 
lower  leaves.  Badly  affected  leaves  fall  away,  leaving  only  a 
bare  stalk.  In  mild  cases,  where  the  disease  runs  its  course 
343 


344 


Diseases  of  Economic  Plants 


more  slowly,  the  intervals  between  the  different  stages  are 
more  prolonged. 

In  light  sand  the  disease  may  progress  very  rapidly  and 
may  consist  of  two  stages  only,  the  sudden  wilted  condition 
followed  by  speedy  death.  The  final  diagnostic  symptom  of 
the  disease,  however,  as  in  the  case  of  many  other  wilts,  is 
the  darkening  of  the  affected  veins,  which  change  from  the 
normal  white  to  light  brown  or  black.  Though  in  most 
cases  the  plant  dies,  occasionally  one  revives  and  seems  to 


Fig.   183. —  A  variety  of  cotton  resistant  to  I  lie  wilt;  note  the 
complete  failure  of  the  other  varieties.     After  Orton. 


outgrow  the  disease.  In  such  plants  relapses  may  follow, 
showing  somewhat  different  symptoms,  among  them  decay 
of  the  boll,  and  a  different  sequence  of  color  changes. 

Rotation  of  crops  should  be  practiced,  the  diseased  plants 
should  be  pulled  and  burned  to  check  the  spread  of  the 
disease  in  the  soil,  and  in  general  the  recommendations 
given  under  soil  diseases  should  be  followed.  Cotton  follow- 
ing cowpeas  infected  with  root-knot,  is  highly  susceptible. 
Therefore,  only  cowpeas  resistant  to  nematodes  should  be 
used  in  cotton  rotation  (Fig.  177).  The  ultimate  solution  of 
the  question  must  be  in  the  employment  of  resistant  varieties. 


Fiber  Plants  345 

Several  such  have  been  bred  by  the  United  States  Depart- 
ment of  Ao;riciilture. 

Anthracnose  ^™-  ^'^  {Glomerella  gossypii  (South.)  Edg., 
Colletotrichum).  —  The  causal  fungus  of  this  disease  was  first 
described  in  1890.  It  is  very  destructive  in  some  localities 
and  prevails  throughout  a  large  portion  of  the  cotton  belt 
of  the  United  States  and  in  the  West  Indies.  The  estimated 
loss  for  1917  was  2.84  per  cent  or  364,000  bales. 

It  is  most  conspicuous  upon  the  bolls,  where  it  produces 
unsightly  ulcers,  at  first  black,  and  later  covered  with  a  pink 
coating.  The  ulcers  have  dark  brown  to  l^lack,  watery  bor- 
ders and  vary  in  diameter  from  a  few  millimeters  to  an  area 
involving  the  entire  boll.  When  small,  the  spots  are  reddish 
and  slightly  depressed.  Attacks  upon  young  bolls  stop  their 
growth  and  induce  premature  ripening  and  imperfect  open- 
ing, or  the  bolls  may  die  and  decay  without  opening  at  all. 
In  such  bolls  the  fungus  is  found  upon  the  lint  and  seed 
within.  Upon  the  stems  the  fungus  is  limited  mainly  to 
injured  parts,  leaf  scars,  etc.,  and  to  very  young,  tender 
plants,  causing  damping-off.  Here  it  is  accompanied  by 
reddening  and  by  shrinkage  in  longitudinal  lines.  This 
disease  upon  young  plants  usually  follows  the  use  of  dis- 
eased seed.  Upon  old  stems  it  causes  blighting  of  the  bark, 
which  becomes  reddish  brown  and  dies. 

The  attack  upon  the  leaves  as  upon  the  stems  is  mainly 
limited  to  injured  or  weak  parts.  The  seed  leaves,  being 
in  a  state  of  weakness,  are  especially  susceptible  to  the 
fungus,  which  develops  here  with  characters  very  similar 
to  those  on  the  stem  and  the  boll.  The  leaves  sometimes 
have  a  scalded  look,  assume  a  yellowish  or  leaden  green 
color,  wither  and  die,  much  as  though  frosted. 

There  is  evidence  that  the  disease  is  largely  carried  from 
year  to  year  in  the  seed  and  may  he  spread  to  clean  seed, 
also,  in  the  gin.  Therefore,  only  seed  from  health}^  fields  and 
seed  that  has  been  ginned  only  where  healthy  cotton  has  been 
ginned  should  be  used. 

Since  the  spores  on  the  seed  are  short-lived,  cotton  seed 


346  Diseases  of  Economic  Plants 

three  or  four  years  old,  still  of  satisfactory  viability,  is  free 
from  infection.  Crops  should  be  rotated  and  seed  bred  on 
isolated  clean  plats.  Treatment  with  commercial  sulfuric 
acid  to  remove  the  lint  and  kill  the  spores  has  given  some 
success.  Hot-water  seed  treatments  are  also  beneficial 
against  this  and  other  cotton,  seed-borne  diseases.  The 
temperature  should  be  kept  as  nearly  65°  C.  (149°  F.)  as 
possible  for  fifteen  minutes.  Different  varieties  of  cotton 
show  different  resistances  to  heat  and  their  germination 
should  be  tested  after  treatment. 

Boll-rot  "'^''  {Diplodia  gossypina  Cke.).  —  This  is  chiefly  a 
black-rot  of  the  bolls,  which  are  thickly  studded  with  pyc- 
nidia.  These  exude  such  quantities  of  black  spores  as  to 
appear  smutty.  The  entire  contents  of  the  boll  also  turns 
black.  Similar  effects  are  less  common  on  the  stem.  The 
disease  is  cause  of  considerable  loss  in  Louisiana.  Fusarium 
boll-rot  (Fusarium  sps.).  —  This  usually  follows  injury  of 
some  kind  and  the  fungus  is  really  a  saprophyte.  Other  boll- 
rots  are  produced  by  Rhinotrichum,  Volutella,  Sclerotium, 
Olpitrichum,  Botryosphseria,  and  even  by  the  gill  fungus 
Schizophyllum. 

Texas  root-rot  "^  ^''  ^"-'  ^^^  (Ozonium  omnivoruvi  Sh.).  — 
The  first  technical  description  of  this  disease  was  given  by 
Pammel  in  1888.  It  has  since  been  the  subject  of  many 
papers,  and  is  known  to  occur  in  very  destructive  form  in 
Texas,  Oklahoma,  New  Mexico,  and  Arizona,  though  it  has 
not  been  seen  east  of  Texas.  The  estimated  loss  from  this 
root-rot  in  1906  in  Texas  was  about  $3,000,000.  Some 
planters  regard  it  as  a  worse  enemy  than  the  boll  weevil. 

In  this  disease  a  few  of  the  plants  may  wilt  and  dry  up 
in  a  day.  Later,  many  plants  suffer  a  similar  fate,  resulting,  in 
irregular  spots  of  disease  in  the  field,  marked  by  the  presence 
of  numerous  standing,  dead  plants.  The  plants  succumb  with 
marked  rapidity  on  hot  days  following  rain,  not  so  rapidly  in 
continuous  dry  weather.  Especially  after  a  rain,  living 
plants  surrounded  by  dead  ones  may  show  symptoms  of  the 
disease  in  the  form  of  dense  sterile  mycelium  upon  the  tap 


Fiber  Plants  347 

root.  All  diseased  plants  have  diseased  roots  marked  by 
injured  rootlets  and  shrunken  tap  roots,  accompanied  by 
depressed  spots  which  are  at  first  bordered  by  red  dis- 
coloration. The  causal  fungus  is  also  apparent  here,  at 
first  as  a  white  mold  which  later  turns  brown  or  yellow 
and  is  finally  accompanied  by  wart-like  sclerotia.  En- 
largements, from  which  new  roots  are  put  forth,  often  occur 
near  the  soil  surface.  Even  the  lint  of  the  diseased  plants  is 
affected,  the  fibers  being  wider  and  larger,  and  the  spirals 
fewer  and  more  uneven,  than  upon  healthy  plants.  The 
disease  is  truly  of  the  soil,  and  the  affected  soil  centers  en- 
large yearly  as  in  other  soil  diseases.  It  is  subject  to  the 
modes  of  dissemination  suggested  on  page  29. 

Extreme  precaution  should  be  exercised  against  the  use, 
for  the  purpose  of  legume  inoculation,  of  soil  which  may 
possibly  be  infested  with  the  disease.  This  warning  is 
particularly  necessary  in  view  of  the  fact  that  alfalfa  is 
affected  by  the  same  disease,  and  the  causal  fungus  is  now 
present  in  many  alfalfa  fields. 

As  to  treatment,  rotation  with  immune  crops  (see  p.  23) 
in  conjunction  with  deep  fall  plowing  is  recommended. 
To  quote  from  Shear  and  Miles:  "Rotation  with  immune 
crops  at  Terrell,  Tex.,  resulted  as  follows:  1904,  planted  to 
cotton,  about  95  per  cent  of  which  was  killed  by  root  rot; 
1905,  planted  to  corn;  1906,  planted  to  wheat,  followed  by 
sorghum  the  same  season;  1907,  cotton  again  planted, 
with  the  result  that,  as  nearly  as  could  be  estimated,  less 
than  5  per  cent  of  the  cotton  was  dead  at  the  close  of  the 
season. 

"Land  badly  infected  with  the  root  rot  was  plowed  seven 
to  nine  inches  deep  November  11,  1906,  at  Petty,  Tex.  In 
experiment  No.  1  the  deep-plowed  plat  showed  42.75  per 
cent  less  dead  plants  than  the  adjoining  check  plat  which 
received  the  customary  tillage.  In  experiment  No.  2  the 
deep-plowed  plat  showed  43  per  cent  less  dead  plants  than 
the  adjoining  check  plat,  and  in  both  cases  a  much  larger 
amount  of  cotton  was  produced  on  the  dead  plants  on  the 


348  Diseases  of  Economic  Plants 

treated  plats,  because  these  plants  did  not  die  until  later 
than  those  on  the  untreated  plats,  and  therefore  had  greater 
opportunity  to  mature  their  bolls." 

Root-knot  (nematodes).  — See  p.  24.  This  knot  is  par- 
ticularly destructive  on  cotton,  not  only  because  of  the 
direct  injury  it  does,  but  also  because  root-knot  greatly  in- 
creases the  susceptibility  of  the  cotton  to  wilt.  All  means  to 
hold  the  development  of  the  nematodes  in  check  should  be 
employed  (pp.  24-25),  particularly  the  use  of  nematode- 
resistant  varieties  of  cowpeas  in  the  cotton  rotation. 

Minor  diseases 

Frosty-mildew  (Seplocylindriuni  areola  (Atk.)  P.  &  G.).  — 
This  leaf-spot  is  limited  sharply  by  the  smaller  veins,  and 
bears  upon  the  lower  surface  numerous  colorless  spores  upon 
colorless  hyphse,  thus  lending  a  frosted  appearance.  Seen 
from  above,  the  spots  are  light  yellow  or  of  a  paler  green  than 
the  normal  leaf  tissue.  Widespread,  though  not  especially 
destructive,  it  does  not  usually  attract  the  attention  of  the 
planter. 

Leaf-blight  (MycosphoBrella  gossypina  (Atk.)  Earle,  Cer- 
cospora).  —  The  fungus  which  causes  this  disease  was  first 
described  from  Carolina  specimens  in  1883,  at  which  time  its 
presence  was  recognized  in  South  Carolina,  Georgia,  and 
Florida.  The  disease  prevails  in  all  cotton  sections  of  the 
United  States,  appearing  first  in  damp  localities  upon  the 
lower  leaves,  and  with  the  progress  of  the  season,  spotting 
all  of  the  leaves  more  or  less.  The  leaf-spots  appear  at  first 
as  small  red  dots,  which  finally,  as  they  enlarge,  bear  brown 
or  white  centers  with  a  characteristic  red  Iwrder.  A  copious 
development  of  dark  hyphse  upon  the  centers  later  gives 
them  a  blackish  hue,  and  numerous  white  spores  give 
these  hyphse  a  white  coating.  The  old  diseased  centers 
of  the  spots  are  brittle  and  frequently  break  away,  leaving 
perforations.  The  disease  is  widespread  but  unimportant, 
since  it  is  largely  limited  to  weakened  tissues,  especially 
to  spots  produced  by  cotton  mosaic. 


Fiber  Plants  349 

Angular  leaf-spot  ^'"^'  ^"'  (Pseudomonas  malvacearum  EFS). 
—  This  disease  was  first  described  in  1891,  and  is  widely 
distributed  in  the  cotton  producing  states,  in  Natal  and 
the  West  Indies.  The  diseased  areas  appear  as  angular 
leaf-spots  bounded  by  the  veins  and  are  of  a  watery  ap- 
pearance. They  may  be  scattered  over  the  leaf,  or  they 
may  be  nearly  contiguous  and  later  become  confluent, 
resulting  in  irregular  dead  patches.  Frequently  they  are 
most  numerous  adjacent  to  the  main  ribs,  and  result  in 
long,  irregular,  dead,  black  regions.  The  dead  tissue  is 
brittle  and  often  falls  away,  causing  holes  or  ragged  edges. 
Badly  affected  leaves  fall  early  and  loss  of  50  or  60  per  cent 
of  the  leaves  is  not  unusual.  When  on  the  boll,  the  spots 
may  be  a  centimeter  in  diameter,  and  the  seed  may  become 
infected.  Seedlings  from  such  seed  are  stunted  and  the 
stand  poor.  Cankers  occur  on  the  stems  of  young  plants. 
Seed  should  be  taken  only  from  healthy  plants.  Treatment 
of  seed  with  concentrated  sulfuric  acid  to  remove  the  lint, 
followed  by  either  the  mercuric  chlorid  or  the  hot-water 
treatments  may  be  employed  to  advantage. 

Damping-ofif  (Pyfhium  debaryanum  and  other  fungi).  — 
Young  cotton  plants  may  suffer  the  characteristic  soft  rot 
of  dam  ping-off. 

Sore-shin  (Corticium  vagum,  Rhizoctonia) .  —  Primarily 
this  is  an  ulcerous  wound  upon  the  stem  near  the  ground, 
accompanied  by  reddening  or  browning  of  the  leaves.  If 
the  ulcer  enters  deep  into  the  stem,  so  as  to  interfere  with 
the  ascending  sap,  it  may  cause  death,  though  the  wound 
usually  heals  before  the  disease  has  progressed  far.  The 
disease  is  often  caused  by  the  attack  of  Rhizoctonia,  espe- 
cially in  tissues  predisposed  to  such  attack  by  weakness. 
Harrowing,  to  aid  in  drying  the  surface  soil,  to  some  extent 
prevents  the  attack  and  development  of  this  fungus. 

A  similar  disease  may  also  result  from  purely  mechanical 
injuries  caused  by  tools. 

Smut  {Doassansia  gossypii  Lag.)  occurs  on  the  leaves  in 
Equador  and  the  West  Indies.     Rust  {Kuehneola  gossyyii 


350  Diseases  of  Economic  Plants 

(Lag.)  Arth.)  is  reported  on  the  leaves  from  Florida,  Cuba, 
Porto  Rico,  and  British  Guiana.  Cluster-cup-rust  {Mcidium 
gossypii  E.  &  E.).  —  An  outbreak  of  this  disease  occurred  in 
southern  Texas  in  1917,  causing  large  defoliation,  with  an 
estimated  loss  in  yield  of  20  per  cent.  It  is  conunonly  present 
in  the  South  to  a  degree,  but  usually  does  not  assume  destruc- 
tive proportions.  Crown-gall  {Pseudomonas  tumefaciens) 
does  some  injury. 

Mosaic,  black-rust.  —  The  first  signs  of  this  disease  are 
yellowish  spots  which  give  the  leaf  a  checkered  appearance. 
The  discoloration  occurs  first  in  small  areas,  which  are 
roughly  rectangular  owing  to  limitation  by  the  veins,  and 
which  are  situated  at  jioints  most  remote  from  the  main  feed- 
ing veins.  Usually  the  centers  of  these  spots  soon  turn 
brown,  and  the  brown  part  enlarges  and  shows  a  series  of 
concentric  markings.  In  later  stages  these  weakened  areas 
may  be  overgrown  by  Alternaria  or  other  saprophytic  fungi. 
If  very  dark-colored  fungi  grow  upon  these  spots,  they  soon 
become  black-coated  and  take  the  popular  name  "black 
rust." 

Kainit,  used  as  fertilizer,  often  reduces  the  damage  from 
mosaic. 

Red  leaf-blight.  —  This  reddening,  resembling  autumnal 
coloration,  occurs  most  frequently  toward  the  season's  end 
and  is  most  common  upon  poor  soil.  It  is  due  chiefly  to 
lack  of  nourishment. 

Attack  of  mites  produces  a  similar  appearance. 

Shedding.  —  This  occurs  chiefly  following  extremes  of 
either  dry  or  wet  weather  or  following  a  change  from  one  ex- 
treme to  the  other. 


FLAX 

Wilt  ■'^"'^  {Fusarium  lini  Bolley).  —  A  condition  of  soil 
known  as  "flax  sick"  has  prevailed  in  many  sections  of  the 
country  to  such  an  extent  as  to  cause  the  abandonment  of 
flax  culture.    This  is  notably  true  in  Iowa,  Minnesota,  North 


Fiber  Plants  351 

and  South  Dakota.  On  such  soils  flax  plants  are  attacked  at 
any  age,  and  die  early  or  late  according  to  the  time  and  in- 
tensity of  the  infection.  Many  of  the  plants  are  killed  before 
they  appear  above  the  surface  of  the  ground.  Such  field 
spots  become  centers  of  disease;  they  enlarge  throughout  the 
summer,  and  new  plants  sicken,  wilt,  and  die  around  their 
margins,  finally  giving  the  entire  field  a  spotted  appearance. 
Young  plants  wilt  suddenly  and  dry  up,  or  decay  if  the 
weather  is  moist.  Older,  woody  plants  become  sickly  and 
weak,  turn  yellow,  wilt  at  the  top,  and  die  slowly.  Such 
plants  are  easily  pulled  up,  owing  to  their  decayed  root 
system. 

Many  of  the  roots  of  diseased  plants  are  dead  and  have 
a  characteristic  ashen-gray  color.  If  the  plant  is  attacked 
late  in  the  season,  this  gray  color  may  be  limited  to  one  side 
only  of  the  taproot.  In  such  cases  the  leaves  and  branches 
on  the  affected  side  are  blighted.  If  the  disease  is  carried  with 
the  seed  into  healthy  soil,  only  a  few  plants  may  l^e  attacked 
during  the  first  year,  and  such  plants  may  be  very  unevenly 
scattered  throughout  the  field  and  escape  notice  until  late  in 
the  season. 

If  the  weather  favors  the  disease,  each  new  area  of  infesta- 
tion may  increase  sufficiently  to  reach  plants  in  several 
adjacent  drill  rows.  These  infested  areas  are  nearly  al- 
ways circular,  and  enlarge  each  year  that  flax  is  grown 
thereon.  Such  a  spot  1-2  m.  in  diameter  the  first  year 
may  become  2-3  m.  the  second  year.  Thus  only  a  few  years 
are  required  for  the  disease  to  gain  complete  possession  of  a 
field.  The  fungus  not  only  persists  in  a  field  not  sown  to 
flax,  but  the  disease  areas  may  even  enlarge  when  no  flax  is 
present.  When  soil  is  once  infested,  no  way  is  known  to 
render  it  again  suitable  for  flax  culture. 

This  is  essentially  a  soil  disease,  and  it  is  spread  in  the 
ways  suggested  under  soil  diseases,  notably  by  soil  particles, 
drainage  water,  and  especially  by  straw  of  diseased  flax  which 
may  get  into  the  manure.  The  chief  agent  of  dissemina- 
tion, however,  is  the  seed.     In  threshing,  the  spores  of  the 


352  Diseases  of  Economic  Plants 

causal  fungus,  which  are  abundant  upon  the  dead  straw, 
find  lodgment  upon  the  seed,  especially  if  it  be  moist. 

To  prevent  carrying  the  disease  to  land  yet  uninfested, 
all  seed  should  be  disinfected  in  the  following  manner: 

Use  formaldehyde  at  the  rate  of  1  pound  to  40  or  45  gallons 
of  water.  Spread  the  seed  upon  a  tight  floor  or  upon  a  canvas 
and  sprinkle  or  spray  upon  it  a  small  amount  of  the  liquid. 
Shovel,  hoe,  or  rake  the  grain  over  rajiidly.  Repeat  this 
spraying,  shoveling,  and  raking  until  all  of  the  seeds  are 
evenly  moistened,  yet  not  wet  enough  to  mat  or  gum  to- 
gether. Continue  to  stir  the  grain,  so  that  the  mass  may 
become  dry  as  soon  as  possible.  Avoid  any  excess  of  moisture. 
If  flax  seeds  are  dipped  in  the  solution  or  are  allowed  to  be- 
come wet  enough  to  soften  the  coats  so  that  they  stick  to- 
gether, they  are  liable  to  be  considerably  injured  or  even 
killed. 

The  solution  recommended  is  strong  enough  to  kill  all 
seeds  if  they  are  thoroughly  saturated  or  are  allowed  to  re- 
main damp  for  some  hours.  Less  than  one-half  gallon  of 
solution  is  required  to  treat  one  bushel  of  seed.  It  is  well, 
also,  to  burn  all  the  infested  straw  and  to  avoid  too  deep 
planting. 

By  continued  selection  of  seed  from  resistant  plants 
Bolley  has  developed  a  variety  which  is  resistant  to  the 
wilt. 

Damping-off  of  young  plants  may  be  caused  by  Alternaria 
or  CoUetotrichum. 

Rust  {Melampsora  lirii  (DC.)  Tub).  ^ — ^Characteristic 
rust  sori  are  in  evidence  and  in  the  early  season  the  leaves 
are  yellow  or  orange.  Later  black  sori  appear,  chiefly  upon 
the  stems.  Badly  affected  plants  turn  ])rown  and  die  earher 
than  plants  not  rusted.  Large  injury  is  not  usual,  though  in 
1904  and  1905  considerable  damage  was  reported  from  North 
Dakota. 

Dodder  {Cuscuta  epilimim  Weihe)  is  similar  to  the  dodder 
of  legumes.    See  alfalfa. 


Fiber  Plants  353 


HEMP 


Wilt  •'^"  (Botryosphceria  marconii  (Cav.)  C.  &  J,,  Dendro- 
phoma).  —  With  the  attack,  appearing  first  upon  the  outer 
ends  of  the  upper  branches,  the  plant  wilts  rapidly.  The 
foliage  soon  turns  brown  and  dies.  The  disease  seems  to  be  a 
recent  importation  from  China. 


TREES  AND  TIMBER  ^^s-  379 
General  Diseases 
DECAY  IN  LIVE  TREES  ^^^  ^^'^ 

Wood  decay  is  caused  by  fungi.  The  mycelium  penetrates 
through  or  between  the  wood  cells,  producing  enzymes  which 
soften  the  cells  or  disintegrate  the  middle  layer  between 
cells,  thus  destroying  stability  of  the  aggregate  as  by  the 
crumbling  of  the  plaster  or  the  brick  of  a  wall.  Within 
the  tree  this  disintegration  may  occur  either  to  the  heart- 
wood  or  to  the  sap  wood,  or  to  both. 

The  life  of  a  tree  may  be  much  reduced  by  decay  of  the 
heartwood,  the  main  mechanical  support.  Decay  of  the 
sapwood  further  hastens  death  by  interfering  with  the  rise  of 
the  sap. 

Upon  the  living  tree  the  natural  protection  against  fun- 
gous invasion  is  the  bark,  consisting  of  cells  with  specially  re- 
sistant walls;  cutinized  or  supplied  with  resin,  gum,  or  other 
repellents.  Moreover,  the  dead  bark  is  not  generally  nutri- 
tious and  does  not  offer  attractive  invitation  to  the  fungus. 
The  protection  thus  constituted  is  normally  ample;  but  in 
case  of  removal  of  this  natural  protection  and  exposure  of' 
either  sapwood  or  heartwood,  especially  the  latter,  the  path 
is  open,  and  it  is  through  wounds  offering  such  exposure 
that  rot  in  standing  timber  usuall.y  begins.  Such  rots  might 
therefore  be  appropriately  termed  "wound  decays." 

The  fungi  which  cause  these  decays  are,  in  the  main, 
the  larger  fungi  whose  fructification  is  of  the  toadstool  type 
(Figs.  191,  194).  After  the  decay  within  is  well  under  way 
the  spore-bearing  toadstools  appear  upon  the  surface  of  the 
diseased  parts,  and  are  quite  generally  recognized  by  lumber- 
men as  a  sign  of  rottenness  within. 
354 


Trees  and  Timber 


355 


A  branch,  broken  or  sawed  off,  split  by  wind,  bruised 
by  a  falling  tree,   gnawed   by  animals,   pecked  by  birds, 


Fomes  igniarius  upon  live  beech  tree 
After  Atkinson. 


eaten  by  insects,  or  wounded  in  any  way,  may  result  in  the 
exposure  of  heart  or  sapwood  to  the  fungous  spore.  From 
this  point  of  invasion  rot  spreads  in  every  direction.  When 
decay  reaches  the  trunk,  it  spreads  upward  and  downward 


356 


Diseases  of  Economic  Plants 


and  into  all  branches  to  which  it  has  access.  Thus  trees, 
hollow  with  rot,  may  trace  their  downfall  to  infection  of  some 
small  branch  or  bark  wound  months  or  even  years  earlier. 
Trees  bearing  the  sporophores  of  fungi    (conchs  or  toad- 


FiG.  185.  —  Stump  of  limb  improperly  removed.    After 
Ind.  Agr.  Exp.  Sta. 

stools)  are  surely  infected,  while  the  absence  of  such  evidence 
is  no  sign  that  a  tree  is  healthy  since  the  infection  may  be 
very  old  and  the  sporophore  earlier  in  evidence  may  have 
rotted  away. 

The  fungi  involved  in  these  decays  are  manifold.  In 
some  cases  one  species  of  fungus  grows  upon  many  different 
kinds  of  wood.    Other  fungi  are  more  particular  as  to  their 


Trees  and  Timber 


357 


food  supply  and  are  found  upon  fewer  hosts.  They  chiefly 
fall  into  two  groups;  one  bearing  its  spores  upon  gills 
(Fig.  194);  the  other  with  its  spores  borne  in  pores. 
Still  others  bear  their  spores  upon  spines.  In  describing 
the  fructification  of  the  causal  fungi  for  recognition  pur- 
poses it  is  necessaiy  to 
note  especially  the 
stalk  or  stipe,  and  the 
cap  or  pileiis  (Fig.  194). 
A  cap  with  no  stalk  is 
"sessile."  To  deter- 
mine the  particular 
species  of  fungus  that 
is  present,  it  is  usually 
necessary  to  examine 
the  sporophore,  and 
even  then  expert  or 
special  knowledge  is 
needed.*  The  deter- 
mination of  the  species 
of  the  fungus  is,  how- 
ever, not  necessaiy  to 
proper  treatment,  since 
this  is  much  the  same 
for  all. 

Care  should  be  ex- 
ercised in  felling  trees 
to  avoid  injuring  other 
trees.      In    forests    in 


Fig.  ISO.  —  \\'ound  of  proijurly  removed 
limb,  beginning  to  heal  over.  After 
Ind.  Agi'.  Exp.  Sta. 


general,  cull  material  and  infected  standing  trees  should  be 
burned  to  prevent  spore  formation.  Excision  of  the  infected 
tissue  should  be  practiced  in  case  of  especially  valuable  trees. 
When  there  are  pruning-wounds,  apply  an  antiseptic  to  the 
exposed  wound  to  prevent  the  effective  germination  of  spores 
upon  its  surface.     Suitable  antiseptics  are  tar  or  paint. 

*  Useful  books  in  such  classification  are  given  in  the  bibliography, 
Nos.  381-387. 


358 


Diseases  of  Economic  Plant 


Red  heart-rot,  Pecky  heart-rot  ^^^  {Trametes  pini  Fr.)  . — 
In  the  North  this  is  the  most  destructive  tree  rot  affecting 
practically  all  conifers,  invading  the  heartwood,  veiy  rarely 
the  sapwood.     The  wood  is  not  wholly  destroyed  by  the 


Fig.   187.  —  Wound  of  jjroperly  removed  limb  nicely  healed 
over.     After  Ind.  Agr.  Exp.  Sta. 


fungus;  but  series  of  small  holes  with  silvery  lining  are  noted 
in  early  stages.  In  spruce  the  color  of  the  wood  itself  is 
changed  to  a  light  purplish  gray,  later  to  a  reddish  brown 
netted  with  small  black  lines.  Small  patches  of  white  follow, 
which  later  develop  into  holes,  arranged  in  series  to  corre- 


Trees  and  Timber  359 

spond  with  the  annual  rings,  and  as  the  disease  progresses 
result  in  a  series  of  vacant  spaces  separated  only  by  plates. 
In  tamarack  the  decay  finally  destroys  the  plates,  reducing 
the  v.'hGle  wood  mass  to  mere  fiber. 

The  sporophores  may  consist  either  of  brackets  or  of 
extended  sheets  with  shallow,  pit-like  pores  on  the  under 
side.  They  are  cinnamon-brown  on  the  lower  surface  and 
much  fissured  and  broken  on  the  black,  charcoal-like  upper 
surface.  Prevention  is  best  effected  by  proper  thinning, 
removing  diseased  trees,  and  destroying  fruiting  bodies. 

White  heart-rot''^'-'  {Fomes  igniarius  Gill.). — ^  This  is  the 
most  important  and  widespread  of  the  heart-rots,  and  one 
which  has  the  widest  range  of  host  plants.  It  is  known  in 
Alaska,  Canada,  the  United  States,  and  in  South  America  to 
Patagonia,  growing  upon  beech,  aspen,  birch,  poplar,  willow, 
mountain  maple,  sugar  maple,  hornbeam,  white  elm,  butter- 
nut, black  walnut,  oaks,  and  hickory.  It  is  common  on  fruit 
trees,  especially  when  near  forests.  The  amount  of  damage 
done  by  it  is  beyond  estimation.  In  many  cases  almost  the 
entire  timber  stand  is  ruined.  Actual  count  has  shown  from 
90  to  95  per  cent  of  otherwise  marketable  trees  valueless. 

Heart-rot,  while  chiefly  of  the  heartwood,  may,  when 
started,  encroach  upon  the  sapwood,  even  to  the  youngest 
layers,  and  death  may  result  by  weakening  the  tree  to  the 
breaking  point.  The  causal  fungus  enters  through  wounds, 
particularly  broken  stubs,  and  usually  produces  its  sporo- 
phores at  these  points  after  the  rot  has  extended  a  meter  or  so 
in  both  directions  from  the  infection  point.  The  first  sure 
external  sign  of  the  disease  is  the  presence  of  the  sporophores, 
although  sounding  with  the  ax  may  sometimes  be  relied  upon. 

The  sporophores,  numbering  sometimes  as  many  as 
twelve  on  a  tree,  are  shelving,  hoof-shaped  bodies  from 
25  to  30  cm.  wide.  The  upper  surface  is  brown,  in  later 
stages  black,  hard,  smooth,  concentrically  marked  with 
age,  finally  seamed  and  cracked.  The  pores  are  in  layers, 
approximately  annual,  and  the  lower  surface  is  gray  to  red- 
brown. 


360  Diseases  of  Economic  Plants 

The  trunk  in  cross-section  shows  rot  at  the  center;  the 
wood  becomes  soft  and  pulpy.     The  decayed  region  is  ir- 


yZ 


( 


Fig.   188.  —  Fomes  igniarius  upon  maple.    After  von  Schrenk. 

regular  in  outline  and  bounded  by  narrow  black  layers.  The 
tree  is  rarely  hollow,  but  remains  filled  with  the  decayed 
wood.  Young  trees  which  bear  no  dead  branches  to  admit 
the  fungus  are  usually  immune. 


Trees  and  Timber  361 

Infective  material  should  be  burned,  wounds  avoided, 
and  excision  practiced  in  case  of  valuable  trees. 

Red  heart-rot,  Brown-checked  wood-rot  ^^^'  ^^^  (Polyporus 
sulphureus  Fr.).  —  The  conifers,  also  oak,  chestnut,  maple, 
walnut,  butternut,  alder,  locust,  apple,  pear,  cherry,  and 
many  other  trees  are  affected.  It  is  widely  distributed,  de- 
structive, and  is  especially  common  on  shade  and  ornamental 
trees. 

The  many-pored  edible  annual  sporophores  consist  of  a 
series  of  overlapping  shelves,  two  to  twenty  or  possibly  more, 
with  the  upper  surface  in  early  stages  a  bright  orange-red; 
later  they  are  sulphur-yellow  both  above  and  below.  The 
upper  surface  when  bruised  is  brown.  The  sporophore  is 
soft  and  fleshy  when  young,  growing  hard  and  brittle  with 
age.  This  fungus  abounds  on  knots  and  stumps.  The  rotted 
wood  resembles  red-brown  charcoal  and  following  decay 
bears  concentric  and  radial  cracks  due  to  shrinkage.  In  these 
cracks  are  large  sheets  of  fungous  wefts. 

Diseased  trees  should  be  cut  and  l:)in'ned  to  prevent 
infection. 

Piped-rot  (Polyporus  sps.).  —  The  oak,  chestnut,  beech, 
and  birch  are  susceptible  to  this  rot,  which  is  limited  to  the 
heartwood  and  is  characterized  by  irregular,  small,  pocket- 
like patches  of  white  fiber.  These  regions  first  appear  in  the 
wood  as  small,  lenticular  areas  which  increase,  coalesce,  and 
change  into  small  pockets.  These  frequently  become  filled 
with  a  dark,  red-brown  mycelium.  The  speckled  character 
of  the  wood  is  a  distinctive  mark. 

White-rot  (Hydnum  erinaceus  Bull.).  —  Although  ob- 
served upon  many  kinds  of  trees,  oaks  are  chiefly  affected. 
The  rotted  wood  is  soft  and  wet,  with  numerous  holes  full  of 
light  yellow  fioccose  mycelium.  The  fleshy  sporophores  are 
white,  1  to  25-30  cm.  in  diameter,  nearly  spherical,  and 
consist  chiefly  of  immense  numbers  of  white  spines  upon 
whose  surfaces  the  spores  are  borne. 

Heart-rot  •''^^  (Fomes  fulvus  Gill.).  —  In  Missouri  and 
Arkansas  this  heart-rot  is  found  upon  birch  and  a  number  of 


302 


Diseases  of  Economic  Plants 


other  trees.  The  wood  turns  brown,  and  crumbles  under 
pressure.  The  rot  extends  from  3-4  m.  above  and  below  the 
sporophores.    These  are  pore-bearing,  triangular  in  section. 


Fig.  189.  —  Polyporus  sulphurcus  showing  ^. 
tree.    After  von  Schrenk 


effect  upon  wood  of  oak 


The  upper  surface  is  very  hard  and  bears  fine,  irregular 
fissures  parallel  to  the  edge.  When  mature,  the  upper 
surface  is  red-brown.  The  pores  are  barely  visible  without 
a  hand  lens. 

Soft-rot  ^^^  (Polyporus  ohfusus  Berk.).— The  black  oaks 


Trees  and  Timber 


363 


(Q.  marylandica  and  Q.  velutina)  are  chiefly  affected  by  this 
rot,  which  is  found  in  Missouri,  Arkansas,  Iowa,  Tennessee, 
Mississippi,  New  Jersey,  and  Maryland. 


Fig. 


190.  —  Tree  weakened  by  Fomes  fomentarius. 
After  Atkinson. 


The  causal  fungus  enters  through  the  burrows  of  a  wood 
borer.  The  heartwood  turns  light  yellow,  then  white, 
and  becomes  brittle.    Strings  and  sheets  of  white  mycelium 


364 


Diseases  of  Economic  Plants 


are  found  in  the  wood.     Death  results  either  from  diminu- 
tion of  water  supply  or  from  breaking  of  the  trunk. 

Heart-rot,  White  wood-rot  ^'^^  {Fomes  everhartii  (E.  &  G.) 
Schr.).  —  This  closely  resembles  the  rot  produced  by 
Fo7nes   igniarius.    Large,   rusty-brown,   woody  sporophores, 

red-brown  below,  grow 


from  wounds  and 
bear  very  small  pores. 
White-rot  ^'^^  {Poly- 
ponis  sqiiamosus  Fr.). 
—  In  Europe  this  rot 
affects  pear,  oak,  elm, 
walnut,  linden,  wil- 
low, ash,  birch,  beech, 
horse-chestnut,  and 
maple.  In  America  it 
has  been  reported  from 
Minnesota.  The  wood 
li  e  c  o  m  e  s  unusually 
white  and  bears  scat- 
'  "'^^Lrf.-  tered   series    of    white 

lnHHHBtt|H|Kgjg|[L  The  nearly   circular 

^^HHHHHIPB0lli^^  bodies      are 

-■B^^^^^^^^  stalked   and  often   at- 

-  ""^ '    tain    a     diameter     of 

15  cm.     When  young, 
they     are     soft,     but 
later      become       very 
tough.     The    upper    surface  is  scaly  and   rough. 

Sapwood  rot  ^^^  (Fomes  fomentarius  Gill.).  —  This  rot 
abounds  throughout  the  northern  part  of  the  United  States, 
as  one  of  the  most  common  diseases  of  deciduous  trees, 
chiefly  affecting  the  beech  and  birch. 

Decay  begins  in  the  outer  sapwood  and  proceeds  in- 
ward. The  wood  is  marked  by  irregular  black  lines,  the 
boundaries  between  diseased  and  normal  wood.    When  en- 


FiG.  191.  —  Fomes  fomentarius  showing 
hoof-shaped  sporophore.  After  Atkin- 
son. 


Trees  and  Timber 


365 


tirely  rotten,  the  wood  is  soft  and  spongy  and  light  yellow 
in  color. 

The   pore-bearing   sporophores   are   hoof-shaped,   smooth 
above,  and  concen- 
trically ridged  and 
gray.     Below  they 
are  red-brown. 

Rot  (Fomes  ap- 
planatus  Wallr.). — 
The  shelving,  per- 
ennial, pore-  bear- 
ing sporophores  are 
very  large,  woody, 
and  g  r  a  y  i  s  h  -  to 
brown  above,  and 
are  commonly 
found  on  dead 
wood,  as  well  as 
on  live  trees  of 
poplar,  beech,  oak, 
birch,  maple. 

Red-brown  rot^^^ 
(F  0  m  e  s  pmicola 
Fr.),  —  The  causal 
fungus  is  of  world- 
wide distribution 
upon  conifers, 
especially  spruce, 
pine,  fir,  and  hemlock.  It  occurs  also  upon  birches  and 
other  deciduous  trees.  Entrance  is  made  through  wounds. 
The  rotted  wood  is  brittle,  cracked,  and  permeated  by 
numerous  sheets  of  mycelium.  In  early  stages  of  decay 
the  color  changes  from  red-brown  to  dark-brown,  after 
which  small,  irregular,  scattered  white  areas  appear.  The 
sporophores  vary  from  2.5-30  cm.,  averaging  10-15  cm., 
are  bracket-shaped  and  lobed.  The  young  lobes  are 
bright    red    to    pale    yellow,    old    ones    dark    red-brown. 


skmxm 

t^mf'fmwiMm 

:  :-m^ms 

m^BM 

kwSll  lisHr 

•ffl 

w^-  ■  '-^ 

^    •,■.  \  "/T 

^L'-,W  ^vf 

.      '-'i 

i's^s^m^mmi^^m 

Fig.   192.  —  Fomes  applanatus  upon  trunk  of 
dead  tree.     After  Freeman. 


366 


Diseases  of  Economic  Plants 


Fig.  193.  —  Fruiting  body  of  Fomes  pinicola  upon  log  rotted 
by  the  fungus.    After  von  Schrenk, 


Trees  and  Timber  367 

The    lower    surface    is    pale    and    smooth,    watery    when 
bruised. 

Following  is  a  list  of  the  principal  genera  of  wood-rotting 
fungi  with  the  names  of  the  trees  on  which  they  grow.  Such 
as  bear  page  references  are  discussed  on  the  pages  indicated. 


Fungus  Hosts 

Armillaria,  p.  370.  Oak,  apple,  and  trees  in  general. 

Collybia.  Horse-chestnut  and  deciduous  trees  gen- 

erally. 

Daedalea.  Chestnut,  maple,  oak. 

Echinodontium.       Fir,  hemlock,  p.  389,  spruce. 

Favolus.  Deciduous  trees. 

Fistulina.  Chestnut,  oak. 

Fomes,  pp.  359,  Alder,  apple,  arbor-vita3,  ash,  p.  381,  as- 
364.  pen,   balsam,   beech,  birch,   butternut, 

Cottonwood,  currant,  cypress,  elm,  fir, 
goosel)erry,  hemlock,  hickory,  juniper, 
p.  383,  larch,  locust,  p.  391,  maple,  oak, 
olive,  orange,  peach,  pine,  plum,  poplar, 
rose,  sassafras,  p.  402,  spruce,  syca- 
more, walnut,  willow,  and  conifers  and 
deciduous  trees  generally. 

Hydnum,  p.  361.  Apple,  beech,  maple,  oak,  spruce,  and 
deciduous  trees  generally. 

Irpex.  Trees  generally. 

Lentinus.  Aspen,  Ijirch,  i^ine,  poplar. 

Lenzites.  Beech,  fir,  pine,  poplar,  spruce,  and  coni- 

fers and  deciduous  trees  generally. 

Pholiota.  Apple,  oak,  poplar,  and  trees  generally. 

Pleurotus.  Elm,  fir,  maple,  mulberry,  pine,  poplar, 

willow. 

Pluteus.  Deciduous  trees  generally. 

Pol)T)orus,  p.  361.  Alder,  apple,  arbor- vitse,  ash,  balsam, 
beech,  birch,  p.  382,  butternut,  catalpa, 
p.  382,  cedar,  cherry,  chestnut,  elm,  fir, 


368 


Diseases  of  Economic  Plants 


hemlock,  juniper,  p.  384,  larch,  linden, 
locust,  maple,  oak,  orange,  pear,  pine, 
poplar,  Pseuclotsuga,  spruce,  walnut, 
willow,  and  conifers  and  deciduous 
trees  generally. 

Polystictus.  Ash,  catalpa,  mountain  ash,  and  decid- 

uous trees  generally. 

Poria.  Birch,  catalpa,  fir,  hemlock,  juniper,  pine, 

spruce,  and  conifers  and  deciduous 
trees  generally. 

Schizophyllum.        Chestnut,  horse-chestnut,  mulberry, 
many  other  trees. 

Septobasidium.       Apple,  oak,  palmetto,  tupelo,  etc. 

Steccherinum.         White  cedar  (Chamcecyparis) . 

Stereum.  Birch,   larch,    oak,    poplar,   willow, 

drupes  and  pomes. 

Thelephora.  Oak  and  trees  generally. 

Trametes,  p.  358.  Birch,  fir,  hemlock,  larch,  locust,  pine, 
spruce,  willow. 

Tricholoma.  Deciduous  trees. 

Volvaria.  Trees  generally. 


and 


and 


Canker,  gall,  twig-blight.  —  These  diseases  occur  upon 
nearly  all  kinds  of  trees.  Galls  are  swollen  parts,  of  the 
general  character  illustrated  in  Figs.  44-212.  Cankers  are 
bark  diseases  of  varied  extent  (Figs.  10,  14).  Twig-blight 
consists  of  death  of  a  twig  through  disease  (Figs.  30,  214). 
When  occurring  on  valuable  trees,  excision  or  spraying  may 
be  warranted,  but  on  forest  trees,  manifestly  no  such  treat- 
ment is  possible,  and  the  only  recourse  is  to  adopt  general 
sanitary  measures,  particularly  the  burning  of  infective 
material. 

The  principal  causes  of  these  diseases  with  the  hosts  are 
given  below.  Those  with  page  references  are  given  more 
complete  discussion  on  the  pages  indicated.* 

*  References  to  books  where  descriptions  of  these  fungi  may  be  found 
are  given  in  the  bibliography  under  numbers  390-394. 


Trees  and  Timber 


369 


Fungus 
Ascochyta. 
Bacteria. 


Botrytis. 

Cenangium. 

Cronartium. 

Crjrptosporella. 

Cyanospora. 

Cytospora. 

Dasysc5T)ha. 
Diaporthe. 
Diplodia. 
Dothidea. 
Dothichiza. 
Dothiorella. 
Endothia. 
Gymno  sporan- 
gium. 
Myxosporium. 

Nectria. 


Nummularia. 
Phoma     and 

Phyllosticta. 
Physalospora 

(Sphaeropsis). 
Pseudomonas 

tumefaciens. 
Strumella. 
Valsa. 


Hosts 

Spruce. 

Filbert,  p.  389,  mountain  ash,  mulberry, 
p.  393,  oleander,  olive,  pomes,  poplar, 
walnut,  p.  404. 

Fir,  hemlock,  horse-chestnut,  larch,  linden, 
orange,  pine,  Prunus,  spruce,  sycamore. 

Pine. 

Pine,  p.  395. 

Hazel,  p.  389. 

Juniper. 

Chestnut,  maple,  nuilberry,  poplar,  p.  401, 
willow. 

Hemlock,  p.  390,  larch,  pine,  spruce. 

Dogwood,  fir. 

Oak,  p.  394. 

Oak. 

Cottonwood,  poplar,  p.  401. 

Walnut,  p.  404. 

Chestnut,  p.  396. 

Cupressus,  incense  cedar  (Libocedrus) , 
white  cedar  (Chamcecyparis) ,  juniper. 

Apple,  beech,  conifers,  oak,  pear,  syca- 
more, tulip. 

Alder,  apple,  arbor-vitse,  ash,  beech, 
birch,  box  elder,  China  berry,  cherry, 
dogwood, elm, fir,  hazel,  horse-chestnut, 
linden,  maple,  mulberry,  oak,  pine, 
spruce,  walnut,  and  conifers  generally. 

Mountain  ash,  pomes. 

Apple,  juniper,  p.  385,  pine. 

Birch,  chestnut,  oak,  willow,  fir,  pomes, 

mulberry,  elm,  magnolia. 
Apple,  chestnut,  oleander,  peach,  pecan, 

poplar,  quince,  spruce,  willow. 
Chestnut,  oak. 
Alder,  apple. 


370 


Diseases  of  Econo?nic  Plants 


ROOT-ROTS 

Fungi  similar  to  those  that  cause  wood-rot  may  also  at- 
tack the  roots  of  trees  and  thus  cause  death  either  with  or 
without  any  previous  rotting  of  the  trunk  wood.  Prominent 
among  such  diseases  are  the  following: 

Shoe-string  root-rot  ^^^  (Armillaria  mellea  Vahl).  —  The 
fungus  usually  enters  the  root  through  wounds,  and  grows  in 


r  r\' 

11 

V''/W 

•».^ 

£ 

.:j^.^m 

Hk^P 

\  '^J^ 

§»*>mJai^''''i 

1  ■■.:-•:.■'."■:-■,, 

Fig.  194.  —  Armillaria  mellea  attackmg  a  tree.    After  Freeman. 


the  cambium,  through  which  it  spreads  until  it  encircles 
the  tree.  As  its  growth  proceeds  the  layers  adjacent  to  the 
cambium  become  dry,  and  the  top  of  the  tree  is  killed  by 
stoppage  of  its  water  supply.  A  characteristic  accompani- 
ment is  the  profuse  development  of  string-like,  hard,  black 
mycelial  strands  which  permeate  the  soil  near  the  base  of 
the  affected   tree.     From  the  mycelium  around  the  base 


Trees  and  Timber  371 

of  the  tree  rise  the  numerous  white-gilled,  honey-colored 
sporophores,  their  viscid  tops  flecked  with  white;  the  stems 
swollen  and  with  a  ring  (annulus). 

This  disease  may  spread  for  long  distances  through  the 
soil  by  means  of  the  fine  roots  and  infect  neighboring  trees. 
Upon  newly  cleared  land  diseased  roots  of  forest  trees  may 
be  a  source  of  infection  to  fruit  trees  subsequently  grown 
thereon.  The  disease  is  common  to  both  conifers  and  de- 
ciduous trees  and  has  been  particularly  troublesome  on  oak, 
pine,  chestnut,  larch,  sycamore,  poplar,  locust,  hemlock, 
birch,  alder,  maple,  and  orchard  trees. 

Red-rot  ^^^  {Forties  annosus  Fr.).  —  Though  not  very  de- 
structive in  this  country,  this  fungus  has  been  found  on 
pine,  spruce,  fir,  and  other  conifers,  more  rarely  on  deciduous 
trees,  where  it  brings  about  a  brown  or  red-rot  of  the  root 
system,  which  ultimately  results  in  the  death  of  an  affected 
tree.  The  fruiting  bodies  form  small,  cup-shaped  shelving 
or  irregular  masses  on  the  roots  or  around  the  base  of  the 
trunk.  The  fungus  has  also  been  found  gi'owing  on  old,  dead 
trees.  Neighboring  trees  generally  become  infected  from  a 
diseased  tree,  through  the  small  fibrous  roots. 

Red-brown  Root-rot  '■^^^  (Polyporus  sckweinitzii  Fr.).  ^ 
A  destructive  root-rot  of  spruce,  fir,  arbor-vitae,  hemlock, 
larch,  and  pine,  by  weakening  tlie  rocjt  or  trunk,  leads  to  the 
overthrow  of  the  tree  by  wind. 

The  point  of  attack  is  always  the  root,  through  the  heart 
of  which  invasion  is  made  into  the  trunk.  This  often  leads 
to  one-sided  decay  of  the  trunk's  heartwood.  The  wood  is 
rendered  brittle,  yellow,  and  later  of  cheese-like  character, 
so  that  it  can  readily  be  cut  cross  grain  when  wet  or  reduced 
to  a  powder  when  dry. 

The  pore-bearing  sporophores,  which  appear  in  July  or 
August,  are  from  10-35  cm.  across,  growing  either  from  the 
roots  or  the  trunk.  If  from  the  trunk,  they  are  sessile; 
from  the  roots  they  are  stalked.  The  fresh  spore  layer  is  rose- 
colored,  and  turns  dark  red  if  bruised. 

This  disease  is  very  common  throughout  northern  for- 


372 


Diseases  of  Economic  Plants 


ests.  In  Europe,  where  it  is  greatly  dreaded,  it  is  customary 
to  prevent  its  spread  by  trenching.  Groups  of  infected  trees 
and  trees  near  them  may  be  cut  to  advantage  to  protect  other 
trees.     Other  toadstool  fungi  that  cause  root-rot  are  Cli- 


FiG.  195.  —  Log  rotted  by  Polyporus  schweinitzii.    After  von  Schrenk. 


tocybe,  Tricholoma,  and  Septobasidium.    Root-rots  are  also 
due  to  other  fungi,  chiefly  the  following: 

Ozonium  Root-rot  (Ozonium  omnivorum  Sh.).  —  Elm, 
basswood,  oak,  cottonwood,  mesquite,  china  tree,  mulberry, 
apple,  and  pear  are  affected  by  this  rot,  which  has  been  de- 
scribed and  discussed  on  page  23. 


Trees  and  Timber 


373 


Rhizina  on  fir,  pine,  larch,  spruce,  hemlock,  Pseudotsuga, 
chestnut;  Sparassis  on  fir,  spruce,  pme,  larch;  and  Thielavia 
(see  p.  23)  on  catalpa;  Xylaria,  see  p.  53. 

DECAY  OF  DEAD  TREES  OR  DEAD  PARTS 

While  decay  of  dead  trees  cannot  be  regarded  strictly 
as  a   condition   of  disease,   but  rather  as  a  post-mortem 


vi.Ji.C^ 


Fig.  196.  —  Dry-rot  fungus  (Merulius  lacrymans);  on  the  right  the 
mycelium  is  visible  as  white  strings.    After  Freeman. 


change,  a  word  is  due  on  account  of  its  vast  importance, 
involving,  as  it  does,  all  structural  wood.  The  fact  that 
the  railroads  purchased  121,402,611  cross-ties  in  the  year 
1915,  and  larger  numbers  in  preceding  years;  that  the  num- 
ber of  posts  in  use  in  1910  was  approximately  4,000,000,000, 


374  Diseases  of  Economic  Plants 

necessitating  an  annual  replacement  of  some  500,000,000 
in  the  United  States,  indicates  the  enormous  money  values 
involved. 

Decay  of  timber  is  brought  about  by  agencies  similar, 
sometimes  identical,  with  those  causing  rot  in  living  trees, 
but  cannot  occur  unless  both  moisture  and  oxygen  are  avail- 
able. Decay  can  be  prevented  by  impregnating  the  wood 
with  various  antiseptics,  as  creosote  or  zinc  chloride. *■*'''  ^^^ 
Merely  removing  the  bark  from  posts  increases  their  length 
of  utility. 

A  few  of  the  chief  causes  of  the  decay  of  dead  wood  are  as 
follows : 

Dry-rot  (Merulius  lacrymans  (Jcq.)  Fr.).  —  One  of  the 
most  common  and  destructive  of  all  the  rots  of  structural 
timber,  it  renders  the  wood  spongy  and  brownish.  If  very 
moist,  a  profuse,  superficial,  pure  white  mycelium  may 
develop,  at  first  loosely,  later  in  dense  sheets  or  strands. 
The  sporophores  are  flat,  at  first  white,  later  red,  and  still 
later  yellow-brown.  The  spore-bearing  surface  carries 
shallow  pores  penned  between  folds  and  wrinkles. 

Sap-rot  ^^^  {Polyporus  versicolor  Fr.).  —  In  addition  to 
its  parasitic  life  upon  the  chestnut  and  catalpa,  this  fungus 
grows  as  a  saprophyte  upon  all  kinds  of  deciduous  woods, 
and  is  regarded  as  the  most  serious  of  all  wood-rotting 
fungi  which  attack  the  dead  wood  of  broad-leaf  trees.  It 
destroys  probably  75  per  cent  or  more  of  the  broad-leaf 
species  of  timber  used  for  tie  purposes.  Whenever  such 
species  are  used  for  fencing,  for  posts  or  poles,  or  for  any  pur- 
pose where  they  come  in  contact  with  the  soil,  they  are  sure 
to  be  attacked  sooner  or  later  by  P.  versicolor.  P.  pergame- 
nus  Fr  is  similar  to  P.  versicolor,  and  also  of  great  im- 
portance, appearing  upon  cut  timber  or  on  large  wounded 
surfaces  of  standing  trees,  especially  following  fires.  It 
is  found  throughout  the  United  States  on  all  deciduous 
woods. 

Numerous  genera  and  species  of  fungi  other  than  those 
mentioned  above  can  also  bring  about  similar  changes. 


Trees  and  Timber 


375 


Mistletoe  ^^^  (Phoradendron  and  Razoumofskyd) .  —  While 
not  generally  considered  pests,  these  parasites  under  favora- 
ble weather  conditions  may  become  so,  especially  upon  trees 


Fig.  197.  —  Trees  infesteci  with  mistletoe.    Courtesy  of  the  School 
of  Botany  of  the  University  of  Texas. 

in  lawns  and  parks.  They  usually  attack  the  smaller  branches 
of  the  trees,  and  thus  cut  off  the  nourishment  from  their 
tips  and  eventually  cause  these  portions  to  die.  The  general 
effect  is  to  spoil  the  beauty  of  the  tree.  On  forest  trees  they 
cause  small  diameters,  reduced  height,  and  scraggy  crowns. 


376  Diseases  of  Economic  Plants 

To  destroy  mistletoe  the  infected  branches  should  be  cut 
from  the  trees  and  no  berries  allowed  to  mature,  thus  pre- 
venting dissemination  of  the  pest  by  birds.  Razoumofskya, 
the  dwarf  mistletoe,  is  represented  by  some  eleven  species  in 
the  United  States,  parasitic  on  conifers,  spruce,  pine,  fir, 
hemlock,  larch.  Phoradendron,  or  the  leafy  mistletoe, 
consisting  of  several  species  is  found  on  practically  all  kinds  of 
broad-leaf  trees. 

Witches-brooms.  —  The  production  of  numerous  adven- 
titious buds  may  result  in  the  close,  broomlike  branching 
which  gives  rise  to  this  common  name.  The  condition  is 
prevalent  on  many  kinds  of  trees,  particularly  so  on  the  hack- 
berry,  which  is  rarely  without  the  witches-brooms  in  profu- 
sion. They  are  also  common  on  horse-chestnut,  juniper,  and 
fir.  The  cause  of  this  abnormal  branching  is  a  stimulus  im- 
parted by  insects  (mites) ,  or  by  any  one  of  several  fungi  as  for 
example:  Taphrina,  Gymnosporangium,  Peridermium,  or 
the  Powdery-mildews. 

Slime-flux.  —  This  is  a  term  applied  to  a  condition  in 
which  portions  of  the  tree  are  covered  by  a  slimy,  fermenting, 
wet,  often  foamy,  flow.  This  usually  originates  in  sap  oozing 
from  a  crack  or  other  wound,  often  following  surgical  work, 
and  is  most  in  evidence  when  the  sap  flows  freely.  The 
organisms,  yeast,  bacteria,  or  their  products,  that  induce  the 
fermentation,  may  cause  death  of  neighboring  cells  of  the 
tree  and  result  in  a  chronic  wound,  though  the  injury  is  at 
most  little  more  than  unsightly.  Excision  and  disinfection 
may  be  practiced. 

Damping-ofif  ^^'  ^-'  ^^®  (Corticium,  Pythium,  and  Fusa- 
rium).  —  Coniferous  seedlings  chiefly  are  affected.  Soil 
disinfection  by  sulfuric  acid,  copper  sulfate,  zinc  chlorid,  or 
formalin,  or  when  practicable  by  steam,  are  advised.  See 
p.  460. 

Tree   Surgery  '">'■  ''-'  ^"^^  ^'^ 

Ornamental,  shade,  and  even  nut  and  fruit  trees  are  often 
of  value  sufficient  to  warrant  careful  surgical  treatment  to 


Trees  and  Timber 


377 


prevent  further  inroads  by 
fungi  already  established 
in  them.  The  real  value 
of  surgical  treatments  is 
somewhat  problematical. 
The  practice  is  of  compar- 
atively recent  popularity, 
and  a  long  interval  of  time 
is  necessary  to  determine 
the  amount  of  benefit. 
The  procedure  is  as  fol- 
lows: First,  all  decayed, 
diseased,  or  injured  wood 
or  bark  must  be  removed, 
either  by  severing  a  limb 
entire  or  by  cutting  out 
a  cavity,  in  which  case 
a  mallet,  sharp  gouges, 
chisels,  and  a  knife  are 
needed.  To  reach  all  of 
the  diseased  wood  it  is 
usually  necessary  to  en- 
large the  opening  and  fre- 
quently to  make  one  or 
more  holes  above  or  be- 
low the  main  opening,  or, 
what  is  perhaps  better,  to 
cut  a  narrow  opening  of 
the  required  length.  The 
excavation  should  be  en- 
larged in  all  directions 
until  only  sound,  unin- 
fected wood  is  left.  The 
bottom  of  the  cavity 
should  be  so  shaped  as 
to  provide  drainage.  The 
edges  of  the  cavity  should 


Fig.  198.  —  Detailed  view  of  exca- 
vated and  bolted  cavities.  Above 
cross-section  of  a  young  tree  trunk 
showing  how  the  new  wood  and 
bark  grow  into  an  unfilled  cavity 
from  the  margin.  (The  line  on  the 
wood  indicates  the  amount  of  ex- 
cavating that  would  be  needed  be- 
fore filling  the  cavity.)  3.  —  Cross- 
section  of  a  tree  trunk  showing 
the  manner  of  using  two  single- 
headed  bolts  to  brace  a  cavity. 
After  Collins. 


378 


Diseases  of  Economic  Plants 


be  undercut  so  that  the  fiUing  will  be  held  firmly  in  place, 
but,  lest  they  dry  out,  should  not  be  less  than  three- 
quarters  of  an  inch  thick,  better  an  inch  and  a  half.  If 
there  is  but  little  undercutting,  nails  may  be  driven  into 
the  interior  to  hold  the  filling.  The  final  cutting  around 
the  cambium  should  be  made  with  a  sharp  knife  and  imme- 
diately followed  by  a  coating  of  shellac  covering  the  edges 
of  the  cambium,  bark,  and  sapwood.  In  cavities  more  than 
two  feet  long,  it  may  be  necessary  to  reinforce  the  remaining 
wood  by  bolts  placed  every  18  to  24  inches  at  appropriate 
angles.    After  excision  is  completed,  the  entire  inner  surface 


Fig.  199.  —  Least  objectionable  method  of  an- 
choring guy  wires  to  trees.    After  Stone. 

should  be  disinfected  with  creosote  or  carbolineum,  and  over 
this  a  heavy  coating  of  tar  or  hot  asphalt  applied. 

The  cavity  may  then  be  filled,  using  Portland  cement  and 
sand  (1  to  3)  well  tamped  in,  the  cement  being  put  in  to  form 
blocks  about  12  inches  high  and  separated  by  tarred  roofing 
paper.  The  face  of  the  cement  should  be  trimmed  back  to 
the  level  of  the  cambium.  Instead  of  filling  the  cavity  with 
cement,  a  mixture  of  dry  sawdust  and  asphaltum,  3  or  4 
parts  to  1,  may  be  used,  with  the  advantage  of  greater 
elasticity  to  meet  the  winds.  Or  the  cavity  may  be  left  un- 
filled and  simply  covered  with  a  concrete  layer  with  ap- 
parently equal  advantages  and  much  saving  of  cement. 
Metal  coverings  of  tin  or  zinc  are  sometimes  used,  but  in 
general  are  not  so  desirable.     Shallow  cavities  are  merely 


Trees  and  Timber  379 

excavated  and  disinfected  and  left  without  filling.  Tree 
surgery  should  be  done  in  mild  weather,  when  the  sap  is  not 
running  actively. 

The  necessity  of  surgical  work  can  largely  be  avoided  by 
early  attention  to  wounds  and  especially  by  avoidance  of 
wounds,  and  l\y  the  use  of  proper  tree  protectors  and  care  in 
guying  and  staying  branches  to  prevent  galling  or  constric- 
tion. 

Leaf-spots,  flower-blight.  Numerous  fungi  cause  spotting 
of  leaves  or  disease  of  flowers  of  trees.  These  injuries  are 
in  general  similar  to  leaf-spot,  for  example  of  celery,  tomato, 
and  other  crops  discussed  on  preceding  pages.  Ordinarily  the 
injury  in  forests  is  not  large,  and  treatment  or  even  sanitary 
measures  are  out  of  the  question.  In  the  case  of  valuable 
shade,  nut,  fruit,  or  ornamental  trees,  or  of  nursery  stock, 
spraying  or  dusting  with  fungicide  is  often  advisable.  Only 
the  more  important  of  the  tree  leaf  diseases  are  discussed 
below. 

Following  is  a  list  of  many  of  the  fungi  of  leaf  and  flower 
diseases  of  trees  with  the  hosts  they  most  commonly  infect. 
Page  references  are  to  further  mention  in  other  parts  of  this 
book.* 

Fungus  Hosts 

Acanthostigma.       Hemlock  and  conifers  generally. 
Ascochyta.  Butternut,  oak,  walnut. 

Asterina.  Magnolia,  oak. 

Cercospora.  Ash,   butternut,  catalpa,  linden,  p.  391, 

maple,  pecan,  red-bud,  sequoia,  willow. 
CoUetotrichum.       Magnolia. 
Cylindrosporium.    Alder,  ash,  birch,  elm,  hackberry,  locust, 

maple,  walnut. 
Didymosphaeria.     Catalpa. 
Entomosporium.     Hawthorn. 
Fusicladium.  Pecan,  p.  394. 

*  Books  to  aid  in  the  study  of  these  fungi  are  listed  in  the  bibhography 
under  numbers  390-394. 


380 


Diseases  of  Economic  Plants 


Gloeosporium. 


Gnomonia. 
Gnomoniella. 
Hendersonia. 
Herpotrichia. 

Hypoderma. 

Keithia. 

Leptostroma. 

Leptothyrium. 

Lophodermium. 

Macrosporium. 

Marssonina. 


Microstroma. 

Monochaetia. 

Neopeckia. 

Peridermium. 

Pestalozzia. 

Phleospora. 

Phoma. 

Phyllosticta. 


Piggotia. 

Ramularia. 

Rhytisma. 

Rust  (Uredinales) 


Septogloeum. 


Ash,  beech,  birch,  butternut,  hazel,  hick- 
ory, horse-chestnut,  linden,  maple, 
p.  392,  oak,  pecan,  p.  395,  sycamore, 
willow. 

Elm,  p.  388. 

Hazel. 

Pine. 

Fir,  incense  cedar,  larch,  spruce,  and 
conifers  generally. 

Larch,  pine,  p.  397,  conifers. 

Arbor-vitae,  hemlock. 

Locust. 

Oak. 

Fir,  juniper,  larch,  pine,  p.  398,  spruce. 

Catalpa,  hackberry. 

Ash,  butternut,  p.  382,  chestnut,  p.  388, 
hickory,  oak,  poplar,  p.  402,  walnut, 
willow. 

Hickory,  walnut,  Inga. 

Chestnut,  p.  388,  oak. 

Pine. 

Fir,  hemlock,  pine,  p.  401,  spruce. 

Oak,  spruce,  and  conifers  generally. 

Ehn,  hackberry,  sycamore,  walnut. 

Plr,  pine. 

Ash,  beech,  catalpa,  p.  382,  chestnut, 
ehn,  hackberry,  hickory,  horse-chest- 
nut, p.  390,  linden,  maple,  p.  392,  oak, 
poplar,  sycamore,  willow. 

Ash. 

Ash,  hackberry,  willow. 

Maple,  p.  392,  oak,  willow. 

Ash,  p.  381,  birch,  p.  382,  cottonwood, 
fir,  larch,  mountain  ash,  osage  orange, 
p.  394,  pine,  p.  395,  poplar,  p.  401, 
shadbush,  willow,  p.  405. 

Willow. 


Trees  and  Timber  381 

Septoria.  Alder,    ash,    birch,    chestnut,    dogwood, 

hackberry,  maple,  oak,  pine,  poplar, 
sweetgiim,   sycamore,   walnut,   willow. 

Stigmatea.  Juniper,  sequoia. 

Taphrina.  Alder,  birch,  elm,  hornbeam,  horse-chest- 

nut, maple,  oak,  p.  394,  poplar. 

Venturia.  Ash,  birch,  mountain  ash,  poplar,  willow. 

Powdery-mildews.  —  The  general  character  of  these  dis- 
eases and  modes  of  treatment  are  discussed  on  p.  122.  The  re- 
marks made  above  regarding  leaf-spot  apply  to  the  powdery- 
mildews  as  well.  The  chief  trees  on  which  they  occur  are: 
alder,  ash,  beech,  birch,  butternut,  catalpa,  chestnut,  dog- 
wood, elder,  elm,  hackberry,  hickory,  horse-chestnut,  honey- 
locust,  linden,  locust,  maple,  mulberry,  oak,  p.  394,  pecan, 
p.  394,  poplar,  shadbush,  sycamore,  walnut,  willow. 

Special  Hosts 
ASH 

White-rot  "^"^  (Fomes  fraxinophilus  Peck).  —  In  certain 
localities  in  Missouri,  Iowa,  Oklahoma,  Nebraska,  and  Kan- 
sas this  disease  affects  90  per  cent  of  the  trees.  It  prevails  in 
the  Mississippi  valley  and  east  to  the  Atlantic.  The  heart- 
wood  first  darkens,  and  later  becomes  soft,  pulpy,  and  yel- 
lowish. The  shelving,  pored  sporophores,  5-10  cm.  long 
and  nearly  triangular  in  section,  are  numerous,  chiefly 
near  stubs  or  wounds,  appearing  soon  after  infection.  The 
old,  upper  surface  is  brown  or  black,  and  very  hard.  Trees 
of  any  age  are  susceptible,  but  those  over  10  cm.  in  diameter 
are  most  subject  to  attack.  Diseased  trees  should  be  cut 
down,  or  excision  practiced. 

Rust  {Puccinia  jraxinata  (Lk.)  Arth.),  —  This  is  a  rust 
which  may  be  recognized  by  the  orange-colored  cluster-cups 
upon  the  swollen  parts  of  the  leaves  and  petioles  of  nearly 
all  species  of  ash.  The  winter  condition  is  found  upon 
marsh-grass,  Spartina.  Usually  the  injury  is  not  large,  but 
in  seasons  favorable  to  the  disease  defoliation  may  result. 


382  Diseases  of  Economic  Plants 

ASPEN.    See  poplar. 

BIRCH 

Sapwood-rot  ''*'  {Polyporus  betulinus  Fr.).  —  Several 
species  of  birch  are  affected  by  this  rot,  which  is  of  wide 
distribution  in  the  northern  United  States.  The  fungus  en- 
ters the  sapwood  from  the  bark  through  wounds  or  through 
the  lenticels,  and  progresses  inward.  When  completely  de- 
cayed the  yellowish,  cracked,  diseased  wood  crumbles. 

Rust  (Melampsoridimn  betulince  (Schm.)  Arth.).  —  This  is 
much  like  the  willow  rust.    See  p.  405. 

BUCKEYE.    See  p.  390. 

BUTTERNUT 

Anthracnose  {Gnomon ia  lepfostyla  (Fr.)  C.  &  de  Not. 
Marssonina).  —  The  affected  leaflets  bear  circular,  dead, 
indefinitely  bordered  spots.  The  disease  spreads  very 
rapidly  throughout  the  tree,  and  to  other  trees.  Defoliation 
results. 

CATALPA 

Leaf-spot  {Phylloslicta  catalpw  E.  &  M.).  —  Affected 
leaves  bear  round,  brown  spots,  often  with  a  yellowish 
gray  border.  The  spots,  from  3-6  nmi.  in  diameter,  often 
coalesce  to  form  large  blotches  which  are  fragile,  sometimes 
dropping  from  the  leaf.  Young  leaves  develop  poorly  and 
are  deformed,  while  severe  infection  may  cause  complete 
defoliation  of  the  tree. 

Soft  heart-rot  ^"^  (Polyporus  versicolor  Fr.).  —  The  wood 
at  the  center  of  the  tree  is  discolored  and  disintegrated, 
eventually  becoming  straw-colored  and  soft.  The  sporo- 
phores  appear  near  the  wound  which  afforded  entrance. 
They  are  sessile,  grouped,  soft,  hairy  above  with  alternate 
bands  of  light  and  dark  color.  When  old,  they  are  tough 
with  edges  curled  in.    See  also  p.  374. 


Trees  and  Timber 


383 


CEDAR,  RED  {Juniperus) 

Rusts  ^"^  {Gymnosporangium  sps.). — Several  distinct 
species  of  the  parasite  occur  on  Juniperus,  some  of  which 
produce  the  usual  "cedar-apples,"  others  produce  cankers  or 
witches-brooms  on  the  branches,  or  spots  on  the  leaves. 
They  are  usually  of  but  small  significance  to  the  cedar  tree 
itself  unless  exceptionally  abundant.    See  apple  rust. 


Fig.  200.  —  "Cedar-apple," 


iingus.    Original. 


White-rot  "^"^^  {Fomes  juniperinus  v.  Sch.).  —  In  this  dis- 
ease holes  appear  in  the  heartwood,  extending  longitudinally 
with  a  partition  of  sound  wood  between.  These  cavities 
eventually  may  unite  to  form  tubes  throughout  the  tree. 
The  wood  between  one  cavity  and  the  next  is  not  the  normal 
red,  but  is  somewhat  browned,  and  the  holes  themselves  are 
coated  with  a  brilliant  white  lining.  The  cavities,  partially 
filled  with  a  velvety  reddish-yellow  mycelium,  may  be  from 
4-9  cm.  long.     The  pore-bearing  sporophore  is  hard  and 


384 


Diseases  of  Economic  Plants 


woody,  rough  above,  later  fissured,  yellow-brown  at  the 
margin,  later  deep  brown.  The  pore  layer  is  yellow  to 
brown. 

Red-rot,  pecky-cedar  ^"^    (Polyporus  roseus  Fr.).  —  More 
common  than  white  rot,  this  has  been  observed  in  Missouri, 


Fig.  201. — ^  Cross-cut  of  cedar  log  showing  effect  of 
Fomes  juniperinus.     After  von  Schrenk. 


Arkansas,   Kentucky,  Tennessee,   Virginia,  New  York,  and 
Mississippi. 

The  wood  is  full  of  pockets  of  brown,  brittle  wood,  vary- 
ing from  a  centimeter  to  a  meter  or  so  in  length.    The  sporo- 


Trees  and  Timber 


385 


phore,  formed  in  the  cavities  under  dead  branches,  is  from 
0.5-35  cm.  in  length  by  1  cm.  wide.  The  pore-bearing  layer 
is  flesh-colored. 

This  and  the  preceding  disease  of  the  cedar  taken  together 
have  been  estimated  to  cause  60  per  cent  loss  in  some  local- 


Fici.  202. 


Longitudinal  section  of  cedar  showing  effect  of  Fomes 
juniperinus.    After  von  Schrenk. 


ities.  Since  they  are  caused  by  wound  parasites,  the  removal 
of  diseased  trees  and  the  destruction  of  sporophores  is 
recommended. 

Cedar  canker  (Phoma  sp.).  —  This  canker  is  found  on 
juniper  and  arbor-vitse.  Injury  apparently  occurs  only  on 
trees  under  four  years  old.  Prior  to  that  age  entire  seed  beds 
may  be  destroyed. 


386 


Diseases  of  Economic  Plants 


CHESTNUT 

Bark-disease  ^^^-  *^-  ^^^  {Endothia  parasitica  (Miirrill)  A.  & 
A.).-— First  noted  in  1904  by  Merkel  in  New  York,  this 

disease  has  spread 
with  a  rapidity  and 
destructiveness  with- 
out parallel  in  plant 
pathology.  Its  dis- 
tribution in  1918  is 
indicated  in  Fig.  205. 
The  disease  extended 
by  natural    agencies 


Fig.  203 


■  Chestnut-bark 
Beattie. 


Fig.  204.  —  Chestnut- 
bark  disease,  show- 
ing the  sporiferous 
pustules.  After  U. 
S.  Bur.  PI.  Ind. 


through   the   native    chestnut  forests  from  Maine  to  Vir- 
ginia, but  shipments  of  nursery  stock  have  been  responsi- 


Trees  and  Timber 


387 


ble  for  its  spread  to  distant  points,  to  British  Columbia, 
California,  Nebraska,  etc.  In  most  of  these  new,  distant 
foci,  the  disease  has  since  been  eradicated.  In  Brooklyn 
16,695  trees  were  killed  on  350  acres,  and  the  loss  in  and 
about  New  York  City  in  1908  was  placed  at  from  $5,000,000 
to  $10,000,000.  The  total  damage  prior  to  the  year  1911  is 
conservatively  placed  at  $25,000,000,  and  may  now  aggregate 


h^ 

tTrVtvn 

\vf}^m 

(        \       /           /                                 1         h 

^^^^^ 

Fig.  205.  —  Distribution  of  chestnut  blight  in  1918.     Courtesy  of  the 
Office  of  Forest  Pathology. 

twice  that  amount,  but  this  is  insignificant  compared  with 
the  loss  that  will  ensue  in  the  chestnut  forests  of  the  Appala- 
chians. It  has  already  caused  more  damage  to  forest  trees  in 
America  than  any  other  fungus.  The  same  disease  has  been 
found  in  China,  and  it  is  reasonably  certain  that  it  was  intro- 
duced into  the  United  States  from  the  Orient  some  time  prior 
to  1904.  This  pest  is  vigorously  parasitic  on  members  of  the 
genus  Castanea  alone,  and  among  the  species  of  this  genus  the 
Japanese  and  Chinese  varieties  are  highly  resistant.  The 
attack  occurs  upon  the  l)ark  through  wounds,  but  twigs  and 
leaves  are  not  directly  affected.     From  the  point  of  attack 


388  Diseases  of  Economic  Plants 

it  spreads  in  all  directions  until  the  diseased  parts  meet  on 
the  opposite  side  of  the  branch,  thus  girdling  the  twig.  Dead, 
discolored,  sunken  patches  with  numerous  yellow,  orange, 
or  reddish-brown  pustules  are  produced ;  spores  are  extruded 
in  greenish  or  yellow  horns.  Cankers  in  midsummer  may  en- 
large at  the  rate  of  a  half-inch  in  diameter  each  week.  The 
appearance  of  the  fungus  upon  the  trunk  indicates  speedy 
death,  but  if  small  branches  are  first  diseased,  the  tree  may 
continue  to  live  for  a  few  years.  When  once  established,  no 
means  of  checking  this  blight  is  known.  Only  preventive 
measures  can  be  taken,  such  as  destruction  of  diseased  trees 
by  fire,  careful  inspection  of  all  nursery  stock,  and  excision 
in  the  case  of  isolated  trees  which  are  considered  valuable 
enough  to  justify  this  mode  of  treatment.  Every  general 
measure  that  has  been  tried  has  been  abandoned,  and  at 
present  the  outlook  indicates  that  the  disease  will  eventually 
exterminate  the  American  chestnut.  To  the  present  time 
$165,000  has  been  used  by  Federal  appropriation  and 
$282,500  by  states,  $275,000  by  Pennsylvania  alone,  in  com- 
bating this  disease. 

Anthracnose,  leaf-spot  {Marssonina  ochroleuca  B.  &  C).  — 
The  characters  of  this  disease  are  small  bleached  areas  bear- 
ing spore  pustules.  It  has  been  quite  injurious  to  nursery 
varieties. 

Bordeaux  mixture  is  advised. 

Large  leaf-spot  (Monochetia  desmazierii  Sacc).  —  This 
leaf-spot  is  abundant  in  forests,  and  causes  much  loss  of 
vigor  to  the  tree.  It  is  recognized  as  large,  1-5  cm.,  circular 
.  spots  with  irregular  concentric  marking.  No  treatment  is 
feasible  in  forests,  but  isolated  trees  can  be  protected  by 
spraying. 


ELM 

Leaf-spot  ''^^  {Gnomonia  ulmea  (Schw.)  Thm.).  —  The  leaf 
spots  are  1-3  mm.  in  diameter,  and  each  spot  is  seen  to  con- 
tain a  cluster  of  small,  black,  rounded  elevations,  the  cluster 


Trees  and  Timber 


389 


surrounded  by  a  border  of  dead  tissue.  Premature  defolia- 
tion results.  The  disease  is  prevalent  in  all  parts  of  the 
United  States. 


FILBERT,  HAZEL 

Blight  '^''  (Bacteria).  —  A  serious  blight,  which  in  many 
respects  resembles  blight  of  pear,  affects  the  filbert  in  Oregon. 
It  occurs  on  buds,  shoots,  leaves,  and 
as  cankers  on  larger  limbs. 

Black-knot  ^^^  {Cryptosporella  anom- 
ala  (Peck)  Sacc.).  — In  1892  Halsted 
noted  black-knot  as  destructive  to  sev- 
eral hundred  trees  in  New  Jersey,  and 
in  1893  Humphry  described  the  same 
disease  upon  hazel  canes  in  Massachu- 
setts. It  is  characterized  by  numer- 
ous small,  elliptical,  warty  emergences 
upon  the  bark  of  the  diseased  branches. 
The  diseased  portions  are  sunken, 
owing  to  the  contraction  of  the  inner 
bark  to  a  mere  line.  The  girdling  pro- 
duced results  in  death  of  the  affected 
canes  and  general  injury  similar  to 
that  produced  by  plum  knot.  Affected 
branches  should  be  cut  and  burned. 


Fig.  206. —  Elm  leaf- 
spot.    After  Heald. 


HEMLOCK,  WESTERN  {Tsuga  heter- 
ophijlla) 

Heart-rot  ^^^  (Echinodontium  tindo- 
rum  E.  &  E.).  —  The  fungus  enters 
through  wounds,  chiefly  branch  stubs,  and  produces  a 
stringy  brown  rot  of  the  heartwood,  which  extends  to  all 
parts  of  the  tree.  A  single  sporophore  of  the  fungus  on 
the  first  16-foot  log  of  the  tree  trunk  may  be  taken  to  indicate 
that  the  heartwood  is  unmarketable  in  both  the  first  and 
second  logs.  The  position  of  the  largest  sporophore  usually 
indicates  the  region  of  greatest  decay. 


390  Diseases  of  Economic  Plants 

Rust  (Melampsorella  elatina  (A.  &  S.)  Arth,  JEcidium).  — 
This  cluster-cup  fungus  produces  bushy  distortions,  "witches' 
brooms,"  by  causing  profuse  branching  of  the  affected  part 
of  the  tree.  These  abnormal  branches  soon  lose  their  leaves, 
and  cluster-cups  are  produced  upon  them.  The  brooms  are 
perennial  and  increase  in  size  each  year,  in  some  cases  largely 
covering  a  whole  tree  with  the  brooms.  In  such  cases  the 
trees  are  stunted  and  may  even  be  killed.  Infection  may 
be  reduced  by  destroying  the  spore-bearing  branches  or  by 
eliminating  the  alternate  hosts,  Alsine  and  Cerastium. 

Canker  (Dasyscypha  resinaria  (C.  &  P.)  Rehm).  —  Swollen 
cankers  occur  in  the  stems  and  branches,  even  girdling  the 
main  trunk  and  killing  the  tree.  After  the  branch  is  dead  the 
causal  fungus  produces  spores  in  small  disks,  orange-colored 
within,  about  4-6  mm.  wide  and  high. 

HORSE-CHESTNUT,  BUCKEYE 

Leaf-blotch  '*^'-  {Guignardia  a'sculi  (Pk.)  Stew.,  Phyllostida) . 
—  Unsightly  spots  upon  the  leaflets,  and  premature  defolia- 
tion, render  this  the  most  conspicuous  disease  of  this  tree. 
The  brown  spots  are  at  first  circular,  but  as  they  enlarge 
are  limited  by  the  larger  ribs,  thus  becoming  nearly  rect- 
angular. Pycnidia  may  be  seen  by  means  of  a  lens.  This 
is  a  decided  nursery  pest  and  is  also  troublesome  on  park 
plantings. 

Lime-sulfur  or  Bordeaux  mixture  have  much  reduced 
the  spotting.  Dusting  (sulfur,  90  parts,  arsenate  of  lead,  10 
parts)  has  also  proved  effective. 

LARCH 

Mistletoe  ^^^  (Razoumofskya) .  —  This  is  the  chief  enemy 
of  the  western  larch,  attacking  trees  of  all  ages.  If  the  trees 
are  not  killed  they  produce  but  a  poor  grade  of  timber  and 
poor  growth,  and  are  moreover  rendered  liable  to  the  at- 
tacks of  wood-rotting  fungi.  All  larches  infected  with 
mistletoe  should  be  cut,  whether  salable  or  not. 


Trees  and  Timber 


391 


LINDEN 

Leaf-spot  (Cercospora  microsora  Sacc). — Small,  circular 
or  large,  irregular,  dead  spots  of  the  leaf  indicate  the  presence 
of  this  disease.     It  has  been  reported  as  destructive  in  Mas- 


FiG.  207.  —  Mistletoe.   After  U.  S.  Bur.  PI.  Ind. 

sachusetts.  New  Jersey,  and  New  York.  Two  sprayings  in 
Massachusetts  resulted  in  longer  retention  of  the  foliage  and 
lessened  infection. 


LOCUST 

Yellow  wood-rot  "^^^  (Fomes  rimosus  Berk.).  —  From 
Massachusetts  to  New  Mexico,  over  the  entire  black  locust 
territory,  this  heart-rot  prevails.    It  is  a  yellow  rot  extending 


392  Diseases  of  Economic  Plants 

from  the  center  outward  in  radial  lines  through  the  medullary 
rays;  the  hard  flinty  wood  is  reduced  to  a  soft,  yellow,  cheesy 
mass,  spongy  when  wet.  The  pore-bearing,  shelving,  hoof- 
shaped,  sporophores  develop  chiefly  from  the  burrows  of 
the  locust  borers  or  from  stubs.  The  young  portions  are 
light  brown;  older  parts,  dark  to  black  and  fissured.  The 
lower  side  is  dull  red-brown. 

The  rot  ceases  with  the  death  of  the  tree,  and  posts  made 
from  diseased  wood  do  not  continue  to  rot. 


MAPLE 

Leaf-spot  (Phijllosticta  acericola  C.  &  E.).  —  A  large  propor- 
tion of  the  leaf  may  become  involved,  causing  premature 
defoliation  which  materially  lessens  the  value  of  the  tree  for 
ornament  or  shade.  The  silver  maples  are  especially  sus- 
ceptible, and  their  sale  has  thereby  been  reduced.  The  leaf 
spot  was  first  noted  in  1874  and  is  distributed  throughout  the 
United  States.  The  blackish,  subcircular  spots  as  they  en- 
large change  to  brown  and  later  to  dirty  white  in  the  center 
with  black  borders.  Small  black  pycnidia  may  be  seen  in  the 
central  regions  of  the  mature  spots,  which  are  from  10-14  mm. 
in  diameter.  Burning  diseased  leaves  is  recommended,  ac- 
companied by  use  of  Bordeaux  mixture  if  economy  justifies. 

Tar-spot  (Rhytisma  acerinum  Fr.).  —  Thick,  shining, 
irregular  black  spots  1-1.5  cm.  across  appear  on  the  leaves  in 
late  summer  and  cause  them  to  fall  prematurely,  thus  weak- 
ening the  tree.  Considerable  damage  is  often  done  to  nur- 
sery stock.  The  leaves  should  be  raked  together  and  burned 
in  the  fall. 

Leaf-spot  {Rhytisma  punctatum  Fr.).  —  In  this  leaf-spot 
the  causal  fungus  forms  several  small,  black  dots  upon  the 
leaves  as  contrasted  with  the  one  large  black  blotch  of  the 
tar-spot. 

Anthracnose  {Gloeosporium  apocryptum  E.  &  E.).  —  Nur- 
sery maples  have  been  seriously  injured  by  this  anthracnose. 
The  tips  of  leaves  of  pruned  twigs  turn  yellow,  then  blacken 


Trees  and  Timber 


393 


and  die  as  though  frosted.  Young  leaves  and  shoots  are 
killed  and  by  their  death  induce  abnormal  branching,  result- 
ing in  a  compact  head.  The  disease  seems  limited  to  young 
trees. 

Bordeaux  mixture  is  advised  —  three  or  more  sprayings. 


Fig.  208.  —  Maple  tar-spot.    After  Heald. 

Thrombosis  (Verticillium). — -Leaves  wilt  and  branches 
die  due  to  plugging  of  the  veins  by  the  fungus.  Dark  streaks 
show  in  the  wood  of  affected  twigs. 


MULBERRY 

Blight  (Bacterium  niori  B.  &  L.).  — Upon  the  leaf  small, 
reddish-brown   spots,   pellucid   when   moist,   are   produced. 


394  Diseases  of  Economic  Plants 

The  twigs  and  even  entire  trees  are  stunted  and  yellowed. 
Cankers  may  almost  or  quite  girdle  the  stem,  the  diseased 
area  becoming  dark.    Prune  as  for  blight  of  pear. 


OAK 

Leaf-curl  ^^^  (Taphrina  coerulescens  (D.  &  M.)  Tul.). — 
Though  close  kin  to  peach  curl,  only  a  small  proportion  of 
each  leaf,  spots  1-2  cm.  in  diameter,  is  involved.  Defoliation 
may  result  in  extreme  cases,  and  continued  disease  each 
year  may  cause  death.  Affected  leaves  should  be  burned 
and  if  the  tree  value  warrants  it  sprayed  as  for  peach  curl. 
Powdery-mildews  (Microsphcera) .  —  These  appear  late  and 
do  little  harm  except  upon  nursery  stock.  Flowers  of  sul- 
fur or  Bordeaux  mixture  are  useful.  Twig-blight  {Diplodia 
longispora  C.  &  E.)  does  some  injury.   Blight.    See  sycamore. 

OSAGE  ORANGE 

Rust  (Physopella  fid  (Cast.)  Arth.).  —  The  sori  which 
are  scattered  thickly  over  large  areas  of  the  lower  side  of 
the  leaf  are  small,  0.1-0.3  mm.  in  diameter  and  are  pale 
cinnamon-brown.  This  rust  is  known  from  South  Carolina 
to  Texas. 

PECAN  415-  416 

Scab  {Fusicladium  effusum  Wint.). — In  the  Southern 
States,  particularly  Florida,  Louisiana,  Georgia,  Oklahoma, 
and  Texas,  twigs,  leaves,  and  nuts  are  affected  with  a  dark 
green,  smoky,  superficial  growth.  Upon  leaves  and  petioles 
dead  spots,  distortion,  and  defoliation  are  caused.  The  new 
growth  of  twig  is  often  killed,  but  the  greatest  injury  is  to  the 
nuts  which  drop  before  maturity. 

Spraying  with  lime-sulfur  or  Bordeaux  mixture,  or  dusting 
with  sulfur  has  proved  effective. 

Powdery-mildew  {Microsphcera  alni  (Wallr.)  Salm.).  — 
During  certain  years  in  the  South  the  pecan  crop  has  been 


Trees  and  Timber  395 

much  injured  by  this  mildew.  It  is  recognized  as  a  flour-Hke, 
white  coating  and  is  particularly  damaging  to  the  young  nuts. 

Spraying  with  Bordeaux  mixture  or  lime-sulfur  before  the 
fungus  appears  is  effective.  Burning  of  infested  fall  refuse 
is  also  helpful. 

Anthracnose  (Glomerella  cingulata,  Glceosporium) .  —  Large, 
light  brown  to  reddish  blotches  occur  on  the  leaves  and  cause 
them  to  fall.  The  nut  hulls  bear  irregular,  sunken,  black 
blotches  which  may  extend  to  the  whole  surface,  and  which 
eventually  bear  numerous  pink  acervuli.  Many  nuts  fall 
prematurely. 

All  infested  refuse  should  be  burned;  a  dormant  spray  ap- 
plied, another  spraying  given  just  after  the  buds  open,  and 
if  need  be,  one  to  three  additional  sprayings  later. 

Rosette. ^^^'  ^^^  —  From  10  to  20  per  cent  of  the  trees  in 
the  Southeast  are  affected.  The  leaves  at  the  branch  ends 
are  first  yellow-mottletl,  then  die.  Later  the  twigs  die  back 
and  the  trees  are  seriously  weakened.  No  parasite  is  present; 
the  disease  seems  to  result  from  deficiency  of  humus,  footl 
material,  and  moisture,  and  may  largely  be  avoided  by 
use  of  legumes,  and  by  plowing  under  green  cover  crops. 

Die-back  (Botryosphceria  berengeriana  de  Not.).  — -Young 
twigs  die  and  their  surfaces  bear  numerous  black  perithecia. 
Dead  wood  should  be  pruned  out  and  burned.  Pink-mold 
(Cephalothecium  sp.)  affects  the  hulls,  nut,  and  the  embryo. 
It  frequently  follows  scab.  Brown  leaf-spot  (Cercosporafusca 
(H.  &  W.)  Rand.),  Nursery-blight  (PhyUosticta  canjce  Pk.),  a 
kernel-spot  (Coniothyrium)  and  Mistletoe  do  some  damage. 
Pollen-blight  {Microstroma  juglandis  (Ber.)  Sacc.  var.  robus- 
tum  Hig.)  presents  an  interesting  case  of  a  fungus  parasitic 
in  the  anthers. 

PINE 

Blister-rust  ^^^'  ^-°  {Cronartium  ribicola  F.  deW.,  Perider- 
mium) .  —  This  rust  which  has  done  much  damage  in  north- 
ern Europe  on  the  5-leaved  or  white  pines,  of  which  there 
are  some  eighteen  species,   entered  the  United  States  in 


396 


Diseases  of  Economic  Plants 


quantity  from  Germany,  between  1900  and  1909  on  diseased 
pine  seedlings,  though  isolated  cases  occurred  here  prior  to 
those  dates,  even  as  early  as  1892.  It  is  now  known  in 
Maine,    New   Hampshire,   Vermont,    Massachusetts,    Con- 


FiG.  209.  —  Map  showing  general  location  of  pine  blister  infections. 

^       Diseased  white  pines  found  in  1816. 

•       Diseased  currants  and  gooseberries  found  in  1916. 

^     Areas  of  heavily  infected  currants  and  gooseberries, 
i-i.      Centers  of  heavy  infection  where  the  principal  efforts  were  made 
'■"•'^  to  eradicate  diseased  plants. 

(Thiee  centers  of  infection  also  exist  in  Wisconsin  and  Minnesota.) 
Courtesy  of  the  Office  of  Forest  Pathology. 

necticut,  New  York,  Pennsylvania,  Rhode  Island,  New 
Jersey,  Kansas,  Ohio,  Indiana,  Wisconsin,  Minnesota.  The 
alternate  host  is  Ribes  (see  p.  116),  some  twenty-one  species 
of  which  are  susceptible.     In  the  spring,  sporidia  from  the 


Trees  and  Timber  397 

Ribes  telial  stage  of  the  rust  may  infect  pines  on  which  they 
fall.  The  first  external  evidence  of  disease  appears  one  to 
several  years  later.  The  bark  thickens  and  later  pycnia 
develop.  In  the  spring,  secia,  numerous  or  few,  mature  on  the 
swollen  bark  and  free  their  orange-colored  spores.  These 
spores  falling  on  Ribes  produce  the  next  stage  of  the  rust, 
though  they  cannot  directly  infect  pine.  The  rust  is  peren- 
nial in  the  pine,  the  cankers  enlarging  year  after  year.  Trees 
attacked  when  young,  c.  g.,  under  25  years  of  age,  are  liable 
to  be  killed.  Older  trees  may  merely  lose  branches  or  the 
central,  top  shoot.  The  damage  to  white  pines  is  very 
serious.  In  1909  the  value  of  standing  white  pine  was  esti- 
mated at  $600,000,000,  the  sugar  pine  at  $120,000,000.  A 
loss  of  even  1  per  cent  of  this,  which  is  a  low  estimate,  is 
significant. 

In  1912  laws  were  enacted  to  prevent  entry  into  the  United 
States  of  foreign  stock  likely  to  harbor  and  introduce  dan- 
gerous fungi  and  insect  pests.  Rigid  Federal  and  state 
inspection  is  now  exercised  to  prevent  further  spread  of  this 
disease.  Imported  Ribes  and  white  pine  must  be  kept  well 
separated.  If  the  disease  is  present,  all  Ribes  should  be 
removed  from  the  vicinity.  At  the  present  time,  $530,448 
of  Federal  appropriations  and  $267,300  of  state  funds  have 
been  used  to  combat  this  disease. 

Bluing''-^  (Ceratostomella  jnlijera  (Fr.)  Wint.). — The 
characteristic  symptom,  bluing  of  the  sapwood,  begins  in 
August  and  September  after  the  trees  have  been  attacked 
by  beetles.  The  blue  color  starts  near  the  base  of  the  tree 
and  gradually  spreads  upward  until  the  entire  sapwood  be- 
comes blue.  The  presence  of  the  mycelium  of  the  above- 
named  fungus,  which  gains  entrance  through  openings  made 
by  the  beetle  and  is  initiated  by  spores  carried  by  the  beetle 
is  responsible  for  the  color  phenomenon.  Blue  wood  is  as 
strong  as  normal,  green  wood,  is  tougher,  and  when  dry,  it 
will  last  as  long;  but  when  wet,  it  rots  rapidly. 

Leaf-cast  {Hyyoderma) .  —  The  needles  die  from  the  tips 
toward  the  bases,  becoming  first  reddish,  then  gray.    Black 


398 


Diseases  of  Economic  Plants 


lines  which  extend  lengthwise  of  the  leaves  arfe  produced  by 
the  ascus-bearing  organs. 

Premature  defoliation  results. 


Fig.  210.  —  Cronartium  ribicola  on  pine  showing  general  aspect  of 
disease.    After  CoUey. 


Leaf-blight,  twig-blight  (Lophodermium  brachysporum 
Rostr.).  —  In  Maine  the  leaf-blight  has  been  noted  as  de- 
structive to  a  considerable  number  of  small  trees  and  in- 


Trees  and  Timber 


399 


juring  the  lower  branches  of  large  trees;  serious  damage, 
however,  is  not  common. 

Damping-off    {Fusarium   sp.).  —  The   general    characters 
are  those  mentioned  under  damping-off.     It  is  serious  in 


Fig.  211.  —  Cronartium  ribicola  on  pine  show- 
ing sporiferous  pustules.     After  Colley. 


Vermont,  New  York,  Missouri,  and  probably  in  many  other 
states,  killing  the  seedlings  in  nurseries  as  soon  as  they  ap- 
pear above  ground.  The  beds  should  be  given  all  ventilation 
possible.  A  top-dressing  of  sterilized  sand  sprinkled  over  the 
beds  immediately  after  germination  resulted  in  30  per  cent 
of  disease  against  42  per  cent  in  the  untreated  part.  For  dis- 
infection of  soil,  see  p.  460. 


400 


Diseases  of  Economic  Plants 


Rust  {Cronartium  cerebrum.  (Pk.)  H.  &  L.,  Peridermium) .  — 
Swollen  areas  occur  upon  the  branches  and  young  stems 
which  are  gradually  killed.     The  gall-like  growth  sheds  a 


«"•?, 

A 

'^ 

¥ 

y^ 

>'y^g«s*yE^B 

Vk  ^ 

'1^^ 

mB 

^^^^p 

Y^ 

'j^^i 

itaJMwB 

\ 

Fig.  212.  —  Gall  j)rt)(lucc(l  by  Cronartium  (Perider- 
mium) cerebrum  on  pine.    After  Hedgcock. 

profusion  of  orange-colored  spores  each  spring.  Chiefly  by 
its  interference  with  the  sap  current  the  swellings  bring  about 
the  death  of  many  trees.    The  galls  are  perennial  and 


may 


Trees  and  Timber 


401 


persist  for  many  years.     One  stage  of  this  rust  occui's  ui)on 
the  oalvs. 

Rust    {Coleosporiavi  soUdagiiiis  (Schw.)  Thihii.,  Perider- 
mium).  —  Another    species    of    Peridermiuni    occurs    upon 
leaves,  producing  small,  sac-like,  tubular  outgrowths  which 
contain  the  spores.    This  is  a  stage  of 
a  rust  which  appears  later  in  the  season 
upon  golden-rods  and  asters. 

Red-rot  {Fonies  pinicola  Cke.). — 
Upon  dead  trees  this  rot  begins  just 
under  the  bark,  usually  near  the  tree 
top,  often  following  bluing.  The  wood 
is  at  first  wet  and  soggy,  but  soon 
becomes  brittle,  so  that  it  crumbles 
readily.  The  cracks  become  filled  with 
felted  fungous  threads.  The  sporo- 
phores  first  appear  as  fleshy  knots, 
soon  red,  which  widen  to  pore-bearing 
shelves. 


POPLAR,  COTTONWOOD 

Rust  (Melampsora  sps.).  —  This  is 
similar  to  willow  rust.    See  p.  405. 

European-canker  "*--  (Dothichiza  pop- 
ulea  S.  &  B.).  —  Species  of  poplar  and 
Cottonwood  in  nine  states  show  this 
disease.  Death  of  the  cambium  re- 
sults, and  following  this  numerous  can- 
kers and  dead  branches  render  the  trees 
unsightly.  The  disease  was  probably 
recently  imported  on  the  Lombardy 
poplar  from  Europe.  New  stock  should 
be  carefully  inspected.  Infected  wood 
should  be  cut  out  and  burned. 

Canker '"^^  (Cytospora    chnjsosperma    (Pers.)    Fr.).  —  This 
serious  canker  is  prevalent  in  the  southwestern  United  States 


Fig.  213.  —  Pine 
needle,  bearing  clus- 
ter-cup of  rust,  en- 
larged. After  Clin- 
ton. 


402  Diseases  of  Economic  Plants 

on  willow  and  poplar,  the  lesions  occurring  on  the  trunks, 
limbs,  and  twigs,  with  reddish  pycnidia  on  the  dead  areas 
near  the  edge  of  the  canker  or  over  the  entire  dead  surface. 
Strict  inspection  should  guard  against  further  spread  of 
the  disease.  Resistant  varieties  should  be  used,  the  trees 
given  plenty  of  water  and  protected  against  mechanical 
injury. 

Leaf -blight  {Marssonina  populi  (Lib.)  Sacc).  ^ — Primary 
infection  occurs  upon  the  leaves,  resulting  in  small,  3-8  mm., 
circular,  black  dead  spots  which  are  quite  definitely  bordered. 
As  the  leaves  die,  the  patches  upon  the  stems  also  turn  black 
and  die.  Infection  proceeds  to  the  supporting  twigs  and  may 
result  in  dead  patches  of  bark  upon  quite  large  shoots. 

Cutting  and  burning  infected  twigs  is  advised. 

Galls  (Macrophoma  tiimefaciens  Sh.)  occur  on  the  branches. 

RUBBER  '^^ 

Trees  and  shrul)s  that  produce  rubber  are  subject  to 
numerous  destructive  diseases,  among  them  Cankers  due  to 
various  species  of  Nectria,  Corticium,  Fusicladium,  and  Di- 
plodia;  Die-back  {Thyridaria)  which  kills  the  young  shoots; 
seedling  diseases  due  to  Pestalozzia,  Helminthosporium  and 
numerous  leaf  fungi,  and  Root-rot  due  to  Fomes,  Irpex, 
Hymenochsete  and  Poria. 

SASSAFRAS 

Heart-rot  {Fames  ribis  (Sch.)  Fr.).  —  Spaulding  in  1907 
described  this  rot  as  a  serious  injury  to  sassafras  in  Missouri. 
It  is  also  found  upon  stems  and  roots  of  various  shrubby 
plants,  as  rose  and  currant.  By  means  of  a  wound  the  attack 
is  made  upon  exposed  heartwood,  proceeding  slowly  into  the 
sapwood.  The  sassafravs  is  thus  immune  until  it  reaches  an 
age  bearing  heartwood.  The  decaying  wood  is  abnormally 
light  in  color  and  slightly  reddish,  and  the  affected  region  is 
bounded  by  a  narrow  black  zone.  Trees  sometimes  die  from 
the  attack. 


Trees  and  Timber 


403 


The  causal  fungus  has  been  reported  in  America  from 
Kansas,  Missouri,  New  York,  and  New  Jersey. 


SYCAMORE 

Blight  (Gnomonia  veneta  (S.  &  S.)  Kleb.,  Gloeosporium) .  — 
First  noted  in  1848,  this  anthracnose  is  very  widely  dis- 
tributed on  sycamore  and  oak 
from  New  Jersey  to  California 
and  Mississippi.  In  extreme 
cases  it  may  so  weaken  the  trees 
as  to  cause  their  death.  The 
scorched  appearance  of  the 
leaves  and  defoliation  render 
the  trees  unsightly.  Just  before 
they  become  full-grown  the 
leaves  give  the  first  indication 
of  the  attack.  Beginning  near 
the  veins  or  ribs  or  upon  the 
petiole,  the  disease  causes  a 
stoppage  of  the  water  supply 
to  the  more  distant  portions  of 
the  leaf,  resulting  in  dead  areas. 

Dead  twigs  should  be  pruned 
out,  and  infected  material  col- 
lected and  burned.  Spraying 
with  Bordeaux  mixture  may  be 
practiced  if  the  expense  is  war- 
ranted. 

WALNUT 

Anthracnose  (Gnomonia  lepto- 
styla  (Fries)  C.  &  d.  Not.  Mars- 
sonina).  —  Conspicuous    brown 

spots,    2^    mm.    in    diameter,  t^        ^..       „r    ,       x     x   • 

^       '                 ,1      ,      .,             ,•  ,  FiG-    214.  —  Walnut     twig 

appear  upon  the  leaflets,  which  blighted  by  bacteria.  After 

soon  yellow  and  fall.    Upon  the  R.  E.  Smith. 


404  Diseases  of  Economic  Plants 

lower  sides  of  the  leaf  spots  arc  small,  concentrically  ar- 
ranged, black  acervuli. 

The  disease  has  been  troublesome  on  black-walnut  in 
Delaware,  Iowa,  Maryland,  and  West  Virginia. 

Blight  ■^-^' '^-^  (Pseudomonas  juglandis  Pierce). — This 
blight  known  in  1901  only  on  the  Pacific  coast  is  now  recorded 
in  California,  Oregon,  Texas,  Louisiana,  Maryland,  Delaware, 
Pennsylvania,  and  New  York  on  English-walnut. 

Black  cankered  spots  upon  the  young  nuts,  which  fall  pre- 
maturely, or  similar  spots  upon  the  young,  green  shoots  are 
characteristic.     Chief  damage  is  to  the  nuts,  l)ut  in  seasons 


Fig.  215.  —  Bacterial  blight  of  walnuts.    After  R.  E.  Smith. 

favorable  to  blight  much  of  the  terminal  growth  is  killed  and 
the  succeeding  crop  is  thereby  reduced. 

Spraying  is  of  questionable  value.  Care  should  be  taken 
to  select  resistant  trees  for  propagation. 

Melaxuma  ^-'^  (Dothiorella  gregaria  Sacc).  —  In  this  dis- 
ease, reported  from  California,  black  sunken  cankers  develop 
on  the  trunk  and  larger  limbs,  and  the  leaves  on  the  smaller 
limbs  suddenly  wilt.  The  first  indication  of  disease  is  often  a 
black  area  like  a  blotch  of  tar  on  the  gray  ])ark.  Excision  and 
disinfection  should  l)e  practiced. 

Other  walnut  troubles  are :  Die-back,  often  due  to  lack  of  or 


Trees  and  Tirnber  405 

excess  of  soil  moisture;  Sun-bum  of  nuts  or  tree  trunk; 
Crown-gall;  Perforation,  an  imperfection  in  shell  develop- 
ment; Root-rot;  Wilt;  Yellows;  and  Leaf-spot  (Marssonina). 

WILLOW 

Rust  (Melampsora  saltciscaprce  (Pers.)  Wint.).  —  Of  tree 
rusts  this  is  one  of  the  most  prevalent,  occurring  as  dusty, 
yellow  sori  upon  the  lower  leaf  surfaces.  Trees  are  rendered 
unsightly  by  the  defoliation  induced.  In  the  latter  part  of 
the  season  the  winter  sori  appear  as  reddish  brown  to  black, 
waxy  or  crusty  spots.  A  similar  rust  is  conmion  upon  cotton- 
wood,  Balm  of  Gilead,  poplar.  Canker  (Cytospora).—See 
poplar. 


ORNAMENTAL  PLANTS 

The  ornamentals  give  rise  to  problems  unique  in  the  field 
of  plant  pathology  due  to  the  fact  that  the  number  of  species 
of  plants  involved  is  much  larger  than  with  any  other  group 
of  crop  plants,  and  moreover,  because  they  vary  greatly  in 
value;  some  of  them,  as  for  example  the  rare  orchids,  have  a 
market  value  higher  than  that  of  any  other  individual  culti- 
vated plant;  other  ornamentals  are  of  negligible  commercial 
value.  There  is  large  diversity  of  financial  interest;  some 
crops  are  grown  on  a  large  scale  by  only  a  few  individuals, 
others  to  considerable  extent  by  nurserjmien  and  seedmen, 
other  crops  are  rarities  in  only  a  few  greenhouses,  while  to 
many  the  flower  garden  in  the  yard  has  a  high  sentimental, 
though  small  money,  value.  Aside  from  a  few  standard 
flowers,  as  for  example  roses,  violets,  chrysanthemums, 
carnations,  etc.,  and  certain  nursery  stock,  so  few  individuals 
are  interested,  or  have  so  small  a  financial  risk  in  these  crops 
that  large  expenditures  of  public  funds  have  not  been  made 
for  investigation  or  control  of  the  diseases.  The  result  is 
that  aside  from  the  standard  ornamental  crops  and  a  few 
isolated  cases  of  other  crops,  the  diseases  have  received  no 
such  complete  study  as  has  been  given  for  example  to  diseases 
of  other  plants  of  general  interest  and  large  commercial 
value.  Indeed  in  many  cases  knowledge  is  limited  to  a  mere 
note  of  the  occurrence  of  certain  diseases  or  parasites,  and  the 
course  of  procedure  is  only  to  ])e  inferred  from  knowledge  of 
similar  diseases.  Flower  fanciers  and  the  conunercial  growers 
of  ornamentals  are  able  and  willing  and  can  well  afford  to  use 
the  best  methods  of  treatment,  and  it  is  unfortunate  that  so 
much  is  lacking  here  concerning  treatment  for  the  specific 
diseases. 

406 


Ornamental  Plants  407 

General  Diseases 

Powdery-mildews.  —  For  description,  see  p.  122. 

These  diseases  are  particularly  common  on  ornamentals  un- 
der glass  or  in  the  open.  The  following  list  comprises  the  hosts 
on  which  they  are  most  frequently  found;  Adonis,  Alyssum, 
Anemone,  Aquilegia,  Begonia,  Berberis,  Calendula,  Chrysan- 
themum, p.  420,  Clematis,  Coreopsis,  Cosmos,  Dahlia,  p.  421, 
golden  glow,  hawthorn,  honeysuckle,  lilac,  p.  426,  larkspur, 
peony,  phlox,  p.  429,  rose,  p.  431,  spirea,  sunflower,  sweet  pea, 
p.  435,  verbena,  p.  436,  violet,  Virginian  creeper. 

In-door  or  out-of-door  treatments  are  essentially  those 
given  under  rose  mildew  (p.  432). 

Cutting-bench  and  Seed-bed  Diseases.  —  If  plants  in  the 
cutting-bench  are  wounded  or  weak  they  are  subject  to  attack 
by  many  fungi  that  could  not  injure  them  under  normal  con- 
ditions. The  chief  point  in  preventing  inroads  by  these  fungi 
is  to  keep  the  cutting-bench  and  seed  bed  in  good  sanitary 
condition,  i.  e.,  proper  degree  of  moisture  and  temperature, 
well  ventilated,  and  free  from  infestation  by  injurious  fungi. 
Soil  and  bench,  if  once  infested,  should  be  disinfected  (p.  460). 
No  diseased  refuse  should  be  allowed  to  contaminate  it.  The 
chief  trouble  in  the  seed  bed  is  damping-off  (p.  19). 

Stem-rot  (Corticium).  —  See  p.  21.  Numerous  plants 
are  affected,  among  them:  Abutilon,  Acalypha,  Achillea, 
Ageratum,  Alyssum,  Amarantus,  Antirrhinum,  Aquilegia, 
Asparagus,  Aucuba,  Bartonia,  Begonia,  Berberis,  Calendula, 
Callistephus,  Campanula,  Celosia,  Centaurea,  Chrysanthe- 
mum, Cineraria,  Coleus,  Coreopsis,  Cuphea,  Dianthus, 
Eriobotrya,  Erysimum,  Euphorbia,  Godetia,  Gypsophila, 
Helianthus,  Hibiscus,  Iberis,  Impatiens,  Iresine,  Kochia, 
Lathyrus,  Lavatera,  Ligustrum,  Linaria,  Linum,  Lobelia, 
Lychnis,  Lythrum,  Matthiola,  Pseonia,  Pelargonium,  Petu- 
nia, Phlox,  Physalis,  Piqueria,  Platycodon,  Portulaca, 
Potentilla,  Primula,  Punica,  Pyrethrum,  Reseda,  Richardia, 
Ricinus,  Salvia,  Santolina,  Schizanthus,  Sedum,  Seradella, 
Silene,  Stachys,  Taxus,  Telanthera,  Verbena,  Vinca,  Viola. 


408  Diseases  of  Economic  Plants 

Slime-mold  {Physanmi,  cinereimi  (Bat.)  Pers.).  —  This 
mold  grows  as  a  slimy  mass  over  any  plants  that  are  in  its 
path,  often  covering  an  area  a  meter  square.  It  later  changes 
to  the  gray,  dusty,  sporing  stage.  It  is  not  really  parasitic  or 
even  injurious,  but  by  its  unsightliness,  arouses  the  apprehen- 
sion of  the  gardener.    No  treatment  is  needed. 

Root-Tot  {Thielavia).  See  p.  23.  Among  the  ornamentals, 
this  disease  has  been  noted  particularly  on  Aralia,  Begonia, 
Cyclamen,  Dahlia,  sweet  pea,  violet,  Tropoeolum. 

Sooty-mold  (Capnodium)  may  occur  on  almost  any  plant, 
though  usually  with  little  or  no  injury.  It  is  most  harmful 
on  the  camelha.  (See  p.  413).  Other  plants  on  which  it  is 
often  seen  are  privet,  Lonicera,  palms,  Cornus,  yew,  oleander, 
rhododendron. 

Crown-gall  (Pseudomonas).  See  p.  87.  Crown-gall  is  not 
usually  troublesome  on  ornamentals.  It  has  been  noted  on 
daisy.  Evonymus,  honeysuckle,  rose,  flowering  almond, 
chrysanthemum. 

Southern-blight  (Sclerotiwn  rolfsii).  See  p.  23.  The  fun- 
gus that  causes  this  disease  may  be  found  on  almost  any 
host,  especially  in  the  South.  Even  as  far  north  as  Illinois 
it  was  destructive  in  gardens  on  Campanula,  Erigeron, 
Dianthus,  Dracocephalum,  Pentstemon,  Phlox,  Eupatorium. 


Special  Diseases 

AGAVE 

Anthracnose  (Colletotrichum  agaves  Cav.). — Spots  are 
produced  on  the  leaves,  and  often  cause  the  death  of  young 
plants.  Diseased  leaves  should  be  removed  and  burned,  and 
the  remaining  leaves  sprayed. 

AMARANTUS  (Various  cultivated  varieties). 

White-rust  (Albugo)  is  common  but  not  serious.  See 
p.  164. 


Ornamental  Plants  409 

ANDROMEDA 

Gall  {Exobasidium  sps.).  —  See  azalea. 

ANEMONE 

Rust  (Cluster-cup) .  —  The  alternate  stage  of  the  rust  of 
drupes  occurs  here.  Drop  (Sclerotinia  tuberosa  Fcl.)  also 
occurs  occasionally. 

ASPIDISTRA 

Anthracnose  (Colleioirichum  omnivorum  Hals.)  is  common 
everywhere  especially  upon  variegated  plants. 

ASTER,  CHINA  (Callistephus) 

Wilt  ^-^'  '^'^~  (Fusarium  conglutinans  Wall.  var.  calUstephani 
Beach.).  —  The  wilt,  mentioned  as  early  as  1896  by  Gallo- 
way, has  since  been  reported  from  Massachusetts  and  Colo- 
rado, and  is  probably  the  most  important  disease  of  the 
China  aster.  The  time  of  transplanting  the  beds  and  blossom- 
ing time  are  most  susceptible  periods,  though  the  wilt  is 
present  to  some  extent  at  other  times. 

The  most  conspicuous  symptom  is  the  sudden  death  of 
the  plants.  The  bark  of  the  stem  is  rotted  at  the  ground  line. 
Close  observation  earlier  shows  the  leaves  upon  one  side  of 
the  plant,  particularly  the  lower  leaves,  yellowed  and  wilted, 
and  the  youngest  leaves  to  be  smaller  than  normal.  The  wilt- 
ing effect  may  sometimes  be  found  first  on  one  side  only  of 
one  of  the  lower  leaves.  Plants  attacked  early  may  die,  or 
in  milder  cases  may  survive  to  produce  a  few  small  blooms. 
If  the  symptoms  first  show  at  blooming  time,  their  sequence 
is  the  same. 

The  roots  in  earl}^  stages  appear  healthy,  -but  the  stem 
near  the  ground,  in  longitudinal  section,  shows  darkening 
of  the  outer  wood,  local  at  first  upon  the  affected  side,  but 
extending  rapidly  in  all  directions.  Eventually  the  dis- 
coloration extends  into  the  bark,  which  rots  away. 


410 


Diseases  of  Economic  Plants 


In  the  seed  bed  the  same  disease  may  occur  as  damping- 
off.  See  p.  19.  It  seems  that  original  infection  always  oc- 
curs in  the  seed  bed,  never  in  the  open. 

Plants  started  in  the  open  are  not  susceptible.  If  it  is 
necessary  to  start  them  under  glass,  too  thick  sowing  should 
be   avoided,    and   they   should   be   ventilated    thoroughly. 

Soil  that  is  known  to  be  in- 
fested should  not  be  used. 
The  disease  may  be  pre- 
vented by  avoidance  of  the 
conditions  that  favor  damp- 
ing-off. 

Yellows. ''^^  —  Growth  is 
spindling  and  the  shoots  and 
leaves  are  yellow,  but  no 
death  of  affected  parts 
occurs.  In  badly  diseased 
plants  no  flowers,  or  only 
rudiments  of  such,  develop 
upon  the  sick  shoots.  In 
other  cases  the  flowers  turn 
greenish-yellow,  wholly  or 
in  part,  with  malformed 
floral  parts  producing  little 
or  no  seed..  No  parasites 
are  present  and  the  cause 
of  the  condition  is  unknown, 
but  the  striking  similarity 
to  peach  yellows  is  obvious. 
The  same  disease  affects  the  marguerite. 

Rust  (Coleosporium  soUdaginis  (Schw.)  Thuem.).  — ■ 
Orange-red  sori,  waxy  in  consistency,  are  produced  in  great 
numbers  upon  the  leaves,  which  when  badly  affected  curl, 
die,  and  thus  bring  about  the  death  of  the  plant.  Stem- 
rot  (Corticium).  — •  See  p.  21. 


Fig.  216.  —  Rust  on  barberry. 
After  Stakman. 


Ornamental  Plants 


411 


AZALEA 

Leaf-spot  (Septoria)  is  common  on  the  leaves.  Gall 
(Exobasidium  sps.).  —  Leaves,  flowers,  or  shoots  are  en- 
larged and  distorted.  Diseased  parts  should  be  cut  and 
burned  and  the  plant  sprayed  with  Bordeaux  mixture. 


BALM,  SILVER 


Rust  (Puccinia  men- 
thce  Pers.).  —  Some 
thirty  species  of  the 
mint  family,  including 
peppermint,  thyme, 
catnip,  monarda,  are 
affected  by  this  rust. 
It  is  recognized  by 
its  sori,  which  are  at 
first  cinnamon-colored, 
later  chestnut-brown. 
Badly  diseased  leaves 
curl  and  die. 

Infested  refuse 
should  be  burned. 

BAMBOO 

Smut  ( Ustilago  shir- 
aiana  Hem.).  —  The 
short  branches  still 
covered  by  the  leaf 
sheaths  are   attacked. 


Fig.  217.  —  Barberry  rust  enlarged. 
After  Stakman. 


Witches-brooms  are  frequently  formed.  It  has  been  found 
in  this  country  on  two  species  of  bamboo.  Diseased  plants 
should  be  burned. 

BARBERRY 

Rust    {Puccinia  graminis,   Mcidium).  —  This   is   of   chief 
interest  on  account  of  the  damage  the  other  stages  of  the 


412  Diseases  of  Economic  Plants 

rust  causes  to  cereals.  Rusts  from  many  grasses  pass  to 
the  common  barberry  though  not  to  the  Japanese  bar- 
berry.    See  p.  277. 

Wilt  {yerticilUum  alboatrum  R.  &  B.)  affects  the  Japanese 
barberry.  The  fohage  turns  yellow  or  red;  the  sapwood  is 
streaked  with  dark  lines;  ultimately  the  wood  turns  black. 
Frequently  the  disease  is  severe. 

BEGONIA 

Eel-worms  in  the  leaves  cause  translucent  watery  spots. 
Powdery-mildew  does  some  harm. 

BLETIA 

Anthracnose  (Colletotrichum  hleticB  Hals.).  —  The  leaves 
of  this  orchid  are  frequently  disfigured  by  very  dark,  almost 
black  spots.  In  late  stages  the  dead  tissue  falls  away,  leaving 
merely  shreds  of  veins  traversing  the  place  of  disease. 

The  tips  of  the  leaves  are  often  frayed. 

Volutella  rot  {Volutella  concentrica  Hals.). — Numerous 
lemon-colored  acervuli  surrounded  by  concentric  bluish 
rings  render  these  spots  different  from  those  above  described. 

CALLA 

Soft-rot  ^"  (Bacillus  carotovorus  Jones).  — A  large  annual 
loss  and  frequently  the  abandonment  of  calla  growing  is  due 
to  this  disease,  which  is  known  throughout  the  United  States. 

The  affected  plants  rot  off  near  the  soil  surface,  and  the 
rot  progresses  from  this  point  up  into  the  leaves  or  down 
into  the  corm.  Usually  the  rot  first  shows  at  the  top  of  the 
corm,  but  in  some  instances  it  is  seen  first  at  the  edge  of  a 
petiole,  or  on  the  corm  below  ground. 

In  section  the  diseased  portion  is  brown,  soft,  and  watery. 
Leaves  whose  bases  are  diseased  become  pale  at  the  edges, 
then  brown.  Similar  changes  occur  in  spots  on  the  leaf,  and 
the  whole  leaf  eventually  dies,  or  the  rot  may  progress  so 
rapidly  that  the  leaf  falls  before  losing  its  green  color.    The 


Ornamental  Plants  413 

flower  or  its  stalk  are  similarly  diseased.  Through  the  corm 
the  roots  are  reached.  Here  the  skin  is  unaffected  and  re- 
mains as  a  parchment-like  tube  filled  with  the  creamy  residue 
of  decay.  Rot  of  the  bulb  may  be  arrested  by  unfavorable 
conditions  and  show  only  as  dark  sunken  spots. 

The  course  of  the  disease  extends  from  a  few  days  to  several 
weeks,  or  the  disease  may  lie  dormant  for  months,  even 
from  season  to  season.  Such  cases  of  dormant  disease  carry 
the  infestation  to  the  succeeding  crop  and  in  commercial 
corms  from  country  to  country.  The  rot  spreads  rapidly 
from  plant  to  plant  by  way  of  the  diseased  roots  and  through 
the  soil  itself.  The  causal  bacillus  remains  in  the  soil  and  may 
attack  healthy  corms  planted  therein  at  later  periods. 

No  known  treatment  of  diseased  plants  is  practicable. 
Infestation  of  soil  may  be  prevented  by  careful  inspection 
of  all  corms  so  as  to  avoid  diseased  ones.  It  is  best  to  test 
commercial  corms  in  pots  to  be  assured  of  their  healthful- 
ness  before  putting  them  in  the  beds.  All  soil  from  badly 
infested  beds  should  be  disinfected  or  removed  and  fresh 
soil  supplied. 

Leaf-spot  {Phijllosticta  richardice  Hals.).  —  Blighted  leaves 
bear  large  ashen  spots  upon  which  are  numerous  minute  dark 
pycnidia. 

Another  Leaf-spot  due  to  Cercospora  richardicecola  Atk. 
was  first  mentioned  by  Atkinson  in  1891  as  occurring  in  Ala- 
bama.    The  edges  of  the  leaves  turn  black  in  circular  spots. 

CAMELLIA 

Sooty-mold  (Capnodium  sp.).  —  The  sooty -mold  is  perhaps 
more  injurious  on  this  plant  than  on  any  other  ornamental, 
not  as  an  actual  disease  but  by  injury  to  salability  of  the  foli- 
age.    Leaf-spot  (Pestalozzia  guepini  Desm.)  is  common. 

CANNA 

Rust  (Puccinia  cannce  (Wint.)  P.  Henn.).  —  This  true  rust 
is  common  and  injurious  in  the  warmer  climates  but  is  rare 
in  the  more  temperate  regions. 


414  Diseases  of  Economic  Plants 

CARNATION 

Rust  ''-^'  ^-"^  (Uromyces  caryophyllinus  (Sch.)  Wint.).  — 
The  carnation  rust  was  first  described  in  1789  in  Germany 
and  was  noted  in  the  United  States  by  Arthur  in  1891, 
evidently  a  recent  importation.  It  rapidly  became  wide- 
spread through  sale  of  infected  plants  and  cuttings  and  was 
soon  present  in  almost  all  greenhouses.  Though  widely 
known  in  Europe,  it  did  not  seem  to  be  especially  destructive 
there;  but  upon  entrance  into  America  its  character  changed 
to  that  of  an  aggressive  pest,  and  ruin  was  brought  to  the 
beds  in  many  greenhouses.  The  entire  contents  of  large 
houses  valued  at  thousands  of  dollars  was  in  many  instances 
utterly  lost.  After  a  short  period  of  extreme  destructiveness, 
which  was  at  its  height  about  1893,  the  vigor  of  the  attack 
waned,  until  to-day  the  pest  does  only  a  small  fraction  of 
damage  as  compared  with  that  of  the  early  years  of  its  inva- 
sion, though  it  still  causes  one  of  the  serious  carnation 
diseases. 

The  rust  is  easily  recognized  b}'  the  sori  filled  with  powdery, 
brown  spores.  The  sori,  at  first  covered  by  the  white  epider- 
mis, are  1-2  mm.  in  diameter,  round  or  elongated  in  the 
direction  of  the  length  of  the  stem  or  leaf.  When  very 
numerous,  the  affected  part  is  slightly  bleached  or  yellowed 
and  appears  swollen,  owing  to  the  much-ruptured  epidermis. 
The  mycelium  of  the  causal  fungus  is  usually  general  through- 
out affected  plants,  but  may,  in  case  of  new  infection,  be 
limited  to  the  immediate  region  of  the  sorus. 

There  is  much  difference  in  varietal  resistance,  a  fact  that 
should  receive  due  weight  in  the  selection  of  varieties  for 
culture. 

Cuttings  should  never  be  taken  from  diseased  stock. 
If  there  is  doubt  as  to  the  presence  of  superficial  spores,  it  is 
well  to  dip  the  cuttings  in  potassium  sulfid,  one  ounce 
to  one  gallon.  A  weekly  protective  spray  of  copper  sul- 
fate, one  pound  to  twenty-five  gallons,  throughout  the  life 
of  the  plant  is  also  recommended.     The  leaves  should  be 


Ornamental  Plants  415 

kept  as  free  from  moisture  as  possible  by  free  ventilation, 
and  still  better  by  subirrigation. 

Fumigation  of  the  houses  in  the  fall  before  the  intro- 
duction of  the  plants  serves  to  lessen  infection  from  old 
spores. 

Rust  sori  are  occasionally  the  seat  of  attack  by  a  Fu- 
sarium,^^^  the  result  being  a  leaf-spot  a  centimeter  or  more 
in  diameter. 

Leaf-spot  (Septoria  dianthi  Desm.).  —  The  spots  of  this 
disease  —  usually  upon  the  leaves,  sometimes  upon  the 
stems  —  are  circular  or  oblong,  blanched  or  pinkish,  and 
purple  bordered.  Numerous  small,  black  pycnidia  lie  in 
the  central  region.  The  disease  is  especially  abundant  upon 
the  lower  portion  of  the  leaves  and  the  sheaths.  The  diseased 
part  often  becomes  contracted,  which  results  in  bending  and 
curling  of  the  leaves.  Surface  watering  of  the  plants  or 
humid  atmosphere  tend  to  increase  the  trouble. 

Another  Leaf-spot  is  due  to  Vermicularia  subeffigiirata 
Schw.  —  The  bases  of  the  leaves  or  the  stems  are  usually  the 
points  of  attack.  Black  spore-bearing  bodies  appear  in 
abundance.  Spraying  with  ammoniacal  copper  carbonate 
has  given  good  results. 

Alternariose  ^^^  (Alternaria  dianthi  S.  &  H.).  —  This  leaf 
and  stem  disease  has  been  reported  as  quite  troublesome 
in  Connecticut,  Pennsylvania,  District  of  Columbia,  North 
Carolina,  Missouri,  and  elsewhere.  It  consists  of  spots 
mostly  upon  the  leaves,  som.etimes  upon  the  stems,  especially 
at  the  nodes.  These  are  strikingly  characteristic,  of  ashen 
whiteness,  with  the  centers  occupied  by  a  scanty,  to  profuse, 
black  fungous  growth.  The  diseased  spot  is  dry,  somewhat 
shrunken,  thinner  than  healthy  portions  of  the  leaf,  approx- 
imately circular,  though  often  somewhat  elongated  in  the 
direction  of  the  longitudinal  axis  of  the  leaf.  When  at 
the  node,  the  disease  usually  involves  the  bases  of  both  of 
the  leaves,  as  well  as  the  stem  between  them.  As  these 
nodal  spots  age,  the  disease  penetrates  through  the  stem, 
killing  its  tissue,  which  shrinks  somewhat  and  becomes  soft 


416  Diseases  of  Economic  Plants 

and  disintegrated,  resulting  in  the  death  of  the  more  distal 
portions  of  the  plant. 

A  striking  feature  is  the  tendency  of  this  disease  to  infect 
to  a  large  degree  one  variety,  the  Mrs.  Thomas  W.  Lawson, 
to  the  exemption  of  others. 

Stem-rot,  wilt  ^^-  (Fusarium  sp.).  —  Described  in  1897  by 
Sturgis,  this  rot  occurs  chiefly  upon  the  stems  and  larger 
branches,  discoloring  the  wood  and  killing  the  bark,  but 
rarely  causing  soft  rot.  The  diseased  plant  dies  gradually 
with  yellowing  and  drying  of  the  foliage,  much  as  though 
due  to  insufficient  water  supply. 

When  practicable,  beds  should  be  disinfected  and  new 
uninfected  stock  introduced.  The  disease  when  first  intro- 
duced upon  a  few  plants  can  be  stopped  by  the  immediate 
removal  and  destruction  by  fire  of  the  diseased  plants. 

Leaf-mold  (Heterosporium  echinulatum  (Berk.)  Cke.).  — 
Circular  spots,  1-4  mm.  in  diameter,  bearing  more  or  less 
concentric  zones  of  dark  mold,  appear  upon  the  leaves,  espe- 
cially the  younger  ones,  also  upon  the  stems  and  sometimes 
upon  the  calyx.  Mold  upon  the  calyx  results  in  deformed 
flower  parts.  In  some  instances  the  whole  top  of  a  plant 
becomes  moldy. 

Infested  refuse  and  leaves  should  be  burned  and  Bordeaux 
mixture  employed  as  a  spray. 

Bacterial-spot  ^^^'  ^'"*  (Pseudomonas  woodsii  (EFS)).  — 
The  spots  of  the  leaves  and  stems  are  small,  usually  sur- 
rounded by  a  narrow  water-soaked  area,  while  the  center  is 
commonly  slightly  brown.  As  the  spots  grow  larger  they 
resemble  Septoria  spots  with  the  exception  of  the  water- 
soaked  margin.  Later  they  dry  and  collapse.  Badly  diseased 
leaves  wither.  In  some  cases  nearly  all  the  leaves  on  many 
of  the  stems  are  so  badly  diseased  as  to  be  hopeless. 

This  trouble  can  be  checked  by  removing  and  burning 
all  diseased  leaves,  then  spraying  with  formalin,  1  part  to  500. 
A  somewhat  similar  spot  caused  by  Aphides  is  known  as 
Stigmonose. 

Gray-mold  {Botrytis  sp.).  —  A  gray-mold  similar  to  that 


Ornarnental  Plants  417 

upon  lettuce  sometimes  attacks  the  carnation  bud,  rotting 
it  before  it  opens. 

Infested  refuse  should  be  burned  and  thorough  ventilation 
provided. 

Bud-rot  ^'"^^  (Sporotrichum  anthophilum  Peck).  —  In  this 
malady  some  buds  never  open,  others  fail  to  expand  to 
perfect  flowers,  still  others  deviate  only  slightly  from  the 
normal.  Badly  affected  flowers,  if  not  picked,  wither  and 
turn  brown  —  first  the  petals,  then  the  sepals.  All  parts  of 
the  flower  within  the  calyx  are  eventually  affected  with  a 
rot,  and  in  som-e  cases,  though  not  always,  hyphae  of  the 
causal  fungus  may  be  seen  with  the  naked  eye.  Mites 
are  usually  present,  but  they  are  not  responsible  for  the 
disease. 

Neglect  is  among  the  prominent  predisposing  causes, 
especially  the  presence  of  too  much  water  in  the  soil  or  air, 
and  the  accumulation  of  debris,  leaves,  trimmings,  and  other 
organic  matter  on  the  benches. 

The  disease  may  cause  considerable  damage;  thus  a  daily 
loss  of  from  $1.50  to  $2  is  recorded  in  one  small  house.  Since 
the  buds  only  are  affected,  not  the  plants  themselves,  no 
permanent  injury  is  done,  and  clean  culture,  destruction  of 
all  refuse  which  might  harbor  the  fungus,  maintenance  of 
moisture  at  the  minimum,  and  the  picking  and  burning  of  all 
infected  buds  will  soon  bring  relief. 

Rot  (Volutella  dianthi  Atk.).  ■ — The  affected  parts  are 
pale  and  studded  with  minute,  black  acervuli.  This  disease 
is  of  greatest  injury  in  the  cutting  bench. 

Stem-rot''-^  {Corticium  vagum). — Plants  suddenly  wilt, 
dry,  and  die,  while  the  outer  portion  of  the  stem  becomes  soft 
and  rotten.  Sclerotia  as  described  in  connection  with  potato 
stem-rot  are  present.  For  further  discussion  of  stem-rot, 
see  p.  21.  High  growing  temperatures  and  excess  of  mois- 
ture should  be  avoided.  Infested  soil  can  be  disinfected  by 
steam. 

Yellows.  —  Irregular,  sunken  spots  occur.  The  cause  is 
unknown. 


418  Diseases  of  Economic  Plants 

CHRYSANTHEMUM 

Leaf-spot  ^•^•''  {Septoria  chrysanthemella  Cav.).  —  Large 
brown  to  black  blotches,  often  irregularly  circular  and  of 
indefinite  border,  appear  upon  the  leaves.  These  enlarge  and 
coalesce  to  involve  the  whole  leaf,  which  withers,  dies,  and 
falls  away. 

The  lower  leaves  are  first  affected,  but  in  later  stages  all 
the  leaves  of  the  plant  may  be  badly  spotted,  and  practically 
complete  defoliation  may  result.  Cuttings  from  infected 
stock  should  be  avoided.  All  diseased  foliage  should  be 
picked,  collected,  and  burned,  and  the  remaining  foliage 
should  be  sprayed  with  Bordeaux  mixture  with  addition  of 
soap  sufficient  to  form  a  suds  to  increase  its  adhesive  power. 
Five  or  six  sprayings  during  the  season  are  usually  sufficient. 
Leaf-spot  (Phyllostida  chrysanthemi  E.  &  D.).  —  This 
disease,  first  described  in  1893, 
is  very  similar  to  the  above,  ex- 
cept that  the  spots  are  more 
regularly  circular,  are  purplish 
brown,  and  have  a  distinct 
border.  Pycnidia  which  may 
often  be  seen  with  the  naked  eye 
are  present. 

Wilt    (Fusarium    sp.)    occurs 
occasionally. 

Rust  ^^^  {Puccinia  chrysan- 
themi Roze) .  —  Apparently  a  na- 
tive of  Japan,  the  rust  was 
introduced  into  England  (1895) 
and  Europe  through  commercial 
agencies,  and  similarly  into  the 
Fig.  218.  —  Chrysanthemum  United  States,  where  it  was  first 
leaf  shoeing  rust  son.    Ong-  ^^^^^  .^  ^^^^  .^  Massachusetts. 

It  was  rapidly  spread  throughout 
this  country  by  diseased  stock,  and  is  now  known  in  nearly 
all  localities  where  the  chrysanthemum  is  cultivated.    The 


Ornamental  Plants 


419 


loss  occasioned  by  the  diminution  in  vigor  of  the  plant  and 
consequent  imperfection  of  bloom  is  large. 

The  sori,  2-3  mm.  in  diameter,  which  are  diagnostic,  first 
appear  as  small  blisters  covered  by  the  epidermis.  The 
rupture  of  this  covering  dis- 
closes a  dark  brown  mass  of 
spores.  The  sori  are  usually 
numerous  upon  the  lower  leaf 
surface,  and  the  spores  form 
dusty  coatings  upon  the 
leaves.  Badly  affected  leaves 
curl;  shrivel,  and  die.  The 
plants  are  dwarfed  and  fail  to 
produce  flowers  of  value. 

All  new  stock  introduced 
to  the  houses  should  be  care- 
fully inspected  and  all  dis- 
eased stock  destroyed  b}^  fire. 
New  stock  should  be  isolated 
and  watched  for  a  month  or 
more  to  be  sure  that  no 
rust  develops.  If  disease  ap- 
pears, all  affected  leaves 
should  be  picked  and  burned 
with  precautions  to  avoid 
scattering  the  spores.  If  the 
rust  continues  to  appear,  all 
parts  above  ground  must  be 
destroyed  by  fire  at  the  end 
of  the  season,  and  plants  for 
the  next  year  raised  in  un- 
contaminated  soil  and  house. 

Ray-blight  ^^^  (Ascochyta  chrysanthemi  Stev.).  — In  this 
disease,  described  by  Stevens  as  doing  considerable  damage 
in  North  Carolina,  the  ray  flowers  are  blighted,  resulting  in 
imperfect  opening  of  the  buds.  Thorough  spraying  with 
Bordeaux  mixture  from  the  beginning  of  the  season  until 


Fig.  219.  —  Chrysanthemum 
blossom  distorted  with  ray- 
blight.     Original. 


420  Diseases  of  Economic  Plants 

blossoming,  accompanied  by  destruction  of  infested  refuse, 
has  proved  a  satisfactory  treatment. 

Powdery-mildew (£'ri/s//>/ie  cichoracearum  DC,  Oidium).— 
This  mildew  occurs  as  white,  flour-like  spots  upon  the  green 
parts  of  the  plant.  It  is  not  often  serious,  but  if  it  should 
become  so,  can  readily  be  controlled  by  the  means  suggested 
for  rose  mildew. 

Leaf-spot  {Cylindrosporium  chrysanthemi  E.  &  D.).  — 
First  described  in  1893,  this- closely  resembles  Septoria  spot, 
though  it  develops  somewhat  more  rapidly  and  is  conse- 
quently more  injurious.  Often  the  leaves  die  and  flowers 
fail  to  form.  Treatment  is  the  same  as  for  Septoria  leaf- 
spot. 

Gall  (Pseudomonas  tumefaciens) .  —  Galls  upon  the  stems 
of  this  plant  have  been  proved  by  Smith  and  Townsend  to  be 
due  to  Pseudomonas.    Treatment  has  not  yet  been  discussed. 

CINERARIA 

Rust  (Coleosporium  senecionis  (Schum.)  Fr.)  is  occa- 
sionally serious. 

CLEMATIS 

Stem-rot  ^^^'  ^^^  (Ascochyta  dematidina  (Thuem.)  Gloy.).  — 
Plants  affected  with  this  disease  were  first  noted  in  1883.  A 
leaf  spot  is  produced ;  the  petioles  are  affected  and  the  fungus 
grows  down  to,  and  girdles  the  stem  at  the  node.  Diseased 
leaves  should  be  removed  and  the  plant  sprayed.  Leaf-spot 
(Cylindrosporium  clematidis  E.  &  E.).  —  This  occurs  on 
clematis  in  propagating  houses  causing  the  loss  of  the  lower 
leaves. 

COLOCASIA 

Rot.^^*^  —  Several  kinds  of  rot  occur  on  the  cormels, 
prominent  among  these  are  the  Java  black-rot  (Diplodia  sps.), 
Powdery  gray-rot  (Fusarium),  Southern  blight  {Sclerotium 
rolfsii),  Soft-rot  (Bacillus  carotovorus) . 


Ornamental  Plants  421 


COSMOS 


Stem-blight^^"  (Phomopsis  stewartii  Pk.).  — The  first 
indication  of  disease  is  seen  in  brown  discoloration  of  the 
stem  or  jjranches,  the  attack  often,  though  not  always, 
occurring  at  a  wound.  The  diseased  branches  at  the  point  of 
attack  are  weak  and  frequently  break  off.  Minute  pycnidia 
are  present  in  the  diseased  parts.  The  disease  appears  only 
on  mature  plants  and  is  very  destructive. 

CYCLAMEN 

Leaf-spot  {Phoma  cydamemB  Hal.).  —  A  disease  of  the 
foliage  which  sometimes  causes  almost  entire  loss  of  the 
crop  is  marked  by  large,  dark,  irregularly  shaped  spots 
upon  the  leaf.  These  spots  later  dry,  turn  lighter  in  color, 
and  show  a  series  of  concentric  light  and  dark  bands,  at  the 
same  time  becoming  brittle  and  often  breaking  away.  Dis- 
eased leaves  should  be  burned  and  the  plants  sprayed  with 
Bordeaux  mixture  or  ammoniacal  copper  carbonate.  Several 
fungi  as  Ascoehyta,  Botrytis,  Phyllosticta,  Ramularia,  Sep- 
toria,  cause  leaf-spots. 

Anthracnose  (Glomerella  cingulata  var.  cydaminis  P.  & 
C).  —  The  spots  on  the  leaves  are  circular,  watery,  with 
definite  borders.  Black,  hairy  acervuli  are  often  present  in 
great  numbers. 

Nematodes  and  Thielavia  occur  on  the  roots. 

DAHLIA 

Powdery-mildew  (Erysiphe  cormnunis  Wallr,  Oidium).  — 
This  powdery-mildew  is  quite  common,  affecting  particularly 
the  lower  leaves  late  in  the  season. 

Blight  {Phoma  dahlia;  Berk.).  —  The  stems  of  the  flowers 
are  the  chief  seats  of  attack.  The  flowers  are  small  and  are 
often  dropped  before  opening.  Root-rot  (Botrytis)  occurs  in 
storage  as  a  wet  soft  rot.  Wilt  {Verticillium  dahlice  Kleb.).  — 
Cf.  p.  180. 


422  Diseases  of  Economic  Plants 

DAISY 

Crown-gall  (Pseudomonas)  does  but  slight  injury. 

DRAC^NA 

Leaf-Spot  (Phyllosticta  maculicola  Hal.).  —  This  may  be 
recognized  as  small,  brown,  somewhat  angular  spots  on  the 
leaves,  each  spot  siu'rounded  by  a  rather  wide  yellow  border. 
Minute  pycnidia  are  present. 

FERNS 

Blight  (Phyllosticta  pteridis  Hal.).  —  The  tender  growing 
tips  of  ferns  are  subject  to  blight,  and  blighted  spots  may  also 
occur  lower  upon  the  leaf.  The  brown  dead  tips  and  leaf 
spots  bear  minute  pycnidia.  Blighted  parts  should  be  cut 
away  and  burned  and  the  remaining  foliage  sprayed  with 
Bordeaux  mixture.  The  disease  is  strictly  local,  and  close 
attention  will  stop  its  spread,  even  after  it  has  considerable 
foothold.  Numerous  other  fungi  are  recorded  on  various 
species  of  ferns,  chiefly  causing  leaf-spots. 

Prothallium-blight  (Completoria  coniplens  Lohde).  —  Upon 
sporelings  (prothallia  of  Aspidium  and  Pteris)  this  disease  is 
first  shown  by  a  yellow  or  yellow-brown  color,  as  seen  in 
mass.  Under  a  hand  lens  the  abnormal  color  is  seen  as  spots, 
varying  from  green  to  yellowish-brown  and  later  to  black. 
In  later  stages  disintegration  of  the  affected  cells  gives  the 
prothallia  a  ragged  appearance. 

GERANIUM  (Pelargonium) 

Gray-mold  (Botrytis  sp.).  —  Frequently  this  mold  appears 
on  old  blossoms,  thence  spreads  to  buds  and  even  to  leaves. 
Proper  sanitation,  destruction  of  all  refuse,  and  attention  to 
ventilation  usually  prevents  this  mold. 

Bacterial  leaf-spot  (Pseudomonas  erodii  Lew.).  —  The 
spots  are  watery,  brown  when  old.    The  affected  leaves  fall. 


Ornamental  Plants  423 


GLADIOLUS 


Hard-rot ''^"  (Septoria  gladioli  Pass.).  —  Leaves  are  af- 
fected with  brown  or  purplish,  irregularly  circular  spots 
having  gray  centers  and  bearing  numerous,  black  pycnidia. 
On  the  corms  lesions  appear  as  water-soaked,  dark  spots 
which  later  become  sunken  and  black.  The  diseased  tissue  is 
extremely  hard.  Spraying  of  seedlings  is  effective,  but  a 
simpler  method  is  to  plant  the  seed  in  soil  that  has  not  borne 
Gladioli,  and  to  bring  to  it  no  infective  material. 

HAWTHORN 

Rust  {Gymnosporangium  sps.).  —  The  rust,  similar  to  that 
of  the  apple,  is  often  abundant. 

HEPATICA 

Rust  {Transchelia,  Mcidium).  —  This  is  perennial  in  the 
plants  which  should  therefore  be  burned  when  the  rust  ap- 
pears.   See  p.  96. 

HIBISCUS,  ROSE-OF-SHARON 

Canker  (Cytospora).  —  Death  of  twigs  or  of  whole  plants 
results.  Diseased  parts  are  thickly  covered  with  wart-like, 
black  pycnidia. 

HOLLYHOCK 

Rust  {Puccinia  malvacearum  Mont.).  — This  rust,  native 
to  Chili,  was  introduced  into  France  about  1868.  It  spread 
rapidly  over  all  Europe,  from  whence  it  came  to  the  United 
States  about  1886  upon  infected  seed.  It  was  rapidly  dis- 
seminated throughout  this  country,  and  is  now  known  from 
Maine  to  Louisiana,  in  many  places  rendering  the  plants  un- 
sightly. It  is  easily  recognized  by  its  yellow  to  brown  sori, 
each  sorus  considerably  raised  above  the  surface  of  the  leaf 


424  Diseases  of  Economic  Plants 

or  stem  as  a  small,  wart-likc  protuberance.  Badly  rusted 
leaves,  or  even  whole  plants,  wither  and  die  as  though 
blighted.  In  mild  cases  the  leaves  remain  green  and  the 
plant  may  bloom. 

It  is  reconmiended  to  sponge  the  diseased  jiarts  with 
permanganate  of  potash:  two  tablespoonfuls  of  saturated 
solution  diluted  with  one  quart  of  water. 

Leaf-spot  [Cercospora  althiiBna  Sacc).  —  Upon  the  leaves 
and  other  green  parts  of  the  hollyhock,  velvet  leaf,  and  mal- 
low rather  large,  dark,  angular  spots  are  produced  in  abund- 
ance, each  spot  with  a  dark  border  and  an  ashen  center  upon 
which  numerous,  black  hyphae  may  be  seen.  Badly  diseased 
leaves  fall,  and  by  midsummer  only  dead,  leafless  stalks  may 
remain.  Even  in  mild  cases,  by  decreasing  the  amount  of 
green  surface,  the  spots  both  injure  the  appearance  of  the 
plant  and  lessen  productiveness. 

Spraying  with  Bordeaux  mixture  or  ammoniacal  copper 
carbonate  at  intervals  of  about  ten  days  is  thoroughly 
effective. 

Leaf-spot  {Phyllosticta  althceina  Sacc).  —  This  pest,  long 
known  in  Europe,  is  recognized  as  large,  brown,  circular 
spots,  1-2  cm.  or  more  in  diameter,  upon  the  leaves.  The 
centers  are  brittle  and  usually  break  away  irregularly. 

Anthracnose  (Colletotrichum  malvarum  (B.  &  C.)  South.). 
—  Since  about  1885,  this  disease  has  been  noticed  in  destruc- 
tive form  in  greenhouses,  particularly  in  the  propagating 
beds;  in  some  cases  to  such  serious  extent  as  to  nearly  pro- 
hibit commercial  culture  of  the  hollyhock.  It  occurs  upon 
any  green  part  of  the  plant.  On  the  leaves  it  forms  brown 
spots  and  causes  withering;  upon  young  succulent  petioles  or 
stems,  collapse  of  the  parts  beyond  follows;  if  the  parts  be 
older,  sunken  spots  varying  from  light  yellow  to  black  are 
produced. 

The  plants  should  be  sprayed  with  Bordeaux  mixture  as 
soon  as  the  first  leaves  appear  and  every  second  day  there- 
after. 

Angular  leaf-spot  (Septoria)  is  also  common. 


Ornamental  Plants  425 

HYDRANGEA 

Leaf-spot  (Phyllosticta  hydrangece  E.  &  E.).  —  Large, 
rusty,  brown  blotches  occur  upon  the  leaves,  in  some 
cases  to  such  extent  that  the  tops  of  the  plants  must 
be  cut  away,  to  the  entire  destruction  of  their  decorative 
value. 

Rust  (Pucciniastrum.  hydrangece  (B.  &  C.)  Arth.)  is  common 
and  often  serious. 

Leaf-spot  (Cercospora  sp.). — Small,  rountl,  or  angular 
white  spots  with  a  very  small  amount  of  dark  hyphal 
growth  in  the  centers  are  common  upon  this  plant.  The 
spots  are  definite  and  are  bordered  by  a  narrow  reddish 
purple  line. 

IRIS 

Leaf-spot  ■'-''  {Didymellina  iridis  (Desm.)  v!  H.,  Heterospo- 
riian).  —  The  disease  occurs  only  on  the  German  iris,  affect- 
ing mainly  the  upper  portion  of  the  leaf  with  oval  spots  with 
water-soaked  margins.  Dead  leaves  should  be  removed  as 
soon  as  the  snow  melts  away. 

IVY  (Hedera) 

Blight  {V ermicularia  trichella  Fr.).  —  This  blight  usually 
begins  midway  between  base  and  apex  of  the  leaf,  and  is 
especially  common  upon  the  white  portions  of  the  variegated 
varieties;  The  diseased  portions  turn  black,  and  small  black 
acervuli  appear. 

LAUREL,  MOUNTAIN  (Kalmm) 

Leaf-blight  {Phomopsis  kalmice  Enl.).  —  Dead  spots  ap- 
pear on  the  leaves  and  may  involve  the  entire  blade,  later  ex- 
tending to  the  stems  and  even  killing  entire  plants.  Leaf- 
spot  {Septoria  kahnicola  (Schw.)  E.  &  E.)  is  of  common 
occurrence. 


426  Diseases  of  Economic  Plants 

LARKSPUR 

A  black  leaf-spot  due  to  bacteria  has  been  noted  in  Massa- 
chusetts. 
Drop  (Sclerotinia) .  —  See  lettuce. 

LILAC 

Powdery-mildew  {Microsphoera  alni  (Wallr.)  Salm.)-  — 
The  characteristic  spots  of  the  powdery-mildew,  white  and 
flour-like,  are  frequent  upon  the  lilac.  Black  perithecia  are 
abundant  late  in  the  season. 

Leaf-spot  (Bacteria)  is  of  minor  consequence. 

LILY 

Gray-mold ''^^  {Dotrytis  sp.).  —  This  exceedingly  destruc- 
tive mold  of  the  lily  was  noted  about  1885,  and  was  first 
closely  studied  by  Ward  in  1888.  It  makes  its  appearance 
in  the  spring  as  small,  orange-colored  spots  upon  the  leaves 
and  buds.  These  enlarge,  and  later  become  coated  with  a 
light  brown,  dusty,  fuzzy  mold  which  destroys  the  leaves  and 
blossoms,  often  leaving  onl}^  the  naked  stalks  standing. 

Sclerotia  much  like  those  described  under  lettuce  drop 
appear  in  association  with  the  decay  in  its  late  stages.  Their 
subsequent  history  is  like  that  of  lettuce  sclerotia. 

Bermuda  lily-disease.^^''  —  The  plants  are  stunted  and  the 
leaves  are  distorted  and  bear  spots  that  are  yellowish  to  white 
and  usually  sunken.  Frequently  a  commercial  loss  of  from 
20  to  60  per  cent  follows.  No  parasite  is  present,  and  the 
actual  cause  of  the  disease  is  unknown.  Rogueing  in  the 
field  to  eliminate  affected  bulbs  is  necessary. 

LILY-OF-THE-VALLEY 

Drop  {Sclerotinia  sps.).  —  See  lettuce, 

MIGNONETTE 

Leaf-spot  ""^^  (Cercospora  resedce  Fcl.).  —  This  disease 
occasionally  ruins  the  greenhouse  crop.     The  spots  are  at 


Ornamental  Plants  427 

first  minute,  pale,  with  brownish  or  yellowish  borders,  or 
they  spread  over  the  leaf  as  a  reddish  discoloration.  In 
late  stages  they  are  uniformly  brown,  with  dark  hyphae 
scattered  over  the  central  portions.  The  dead  areas  enlarge 
irregularly,  and  the  leaves  finally  curl  and  die. 

Bordeaux  mixture  and  ammoniacal  copper  carbonate,  used 
once  a  week,  have  proved  effective  remedies. 

MORNING-GLORY,  MOON-FLOWER 

The  following  are  common  but  usually  not  serious: 

Rust   {Coleosporium  ipomcem  (Schw.)  Burr.);  White-rust 

(Albugo   ipo7noece-pandurance) ;    Leaf -spots    due    to    various 

fungi. 

NASTURTIUM  {Tropoeolum) 

Blight  (Pseudomonas  aptatum).  — •  In  this  disease  the  leaves 
are  wilted  and  bear  water-soaked  spots  usually  about  3-5 
mm.  in  diameter.  Black-mold  (Pleospora  tropocoli  Hal., 
Alternaria).  —  The  leaves  which  are  affected  turn  light  green, 
later  yellow,  and  still  later  are  covered  with  a  black  mold. 

Damping-off  (Colletotrichum).  —  Damping-off  due  to  a 
species  of  Colletotrichum  is  common  in  the  cutting-bed. 
The  diseased  parts  bear  numerous  black  acervuli. 

White-rust  (Albugo  Candida)  occurs  rarely. 

OLEANDER 

Kjiot,  gall  "■''  (Bacillus).  —  This  disease  both  upon  leaves 
and  stems  appears  to  be  identical  in  character  with  that  upon 
the  olive. 

ORCHIDS 

Mold  (Botnjtis).  —  The  presence  of  straw-colored  spots 
often  renders  the  plants  unsightly  and  the  flowers  valueless. 
A  gray  mold  similar  to  that  found  upon  the  lily  appears  later. 

All  infested  refuse  should  be  burned. 


428  Diseases  of  Economic  Plants 

Numerous  anthracnoses,  leaf-spots,  rusts,  and  other  dis- 
eases also  occur  on  orchids.  Their  discussion  would  involve 
many  pages.    See  also,  p.  412. 


PALM 

Anthracnose  {Colletotrichum) .  —  Palms  often  die  and  turn 
black  at  the  tips  of  the  leaf  segments,  or  similar  spots  may 
appear  upon  other  parts  of  the  leaf.  These  spots  near  their 
edges  have  a  watery  appearance.  When  they  become  dry, 
purplish  acervuli  appear.  Upon  seedlings  the  disease  is  par- 
ticularly troublesome,  resulting  in  failure  of  the  leaves  to 
unfold. 

The  blighted  parts  should  ])e  cut  away  and  burned  and  the 
remaining  foliage  sprayed  at  least  once  each  week  with 
Bordeaux  mixture  or  anmioniacal  copper  carbonate. 

Graphiola  blight  {Graphiola  phmiicis  (Mong.)  Poit.).  — 
Small,  gray,  tul:)orcular  growths,  1-2  mm.  in  diameter,  appear 
scattered  over  the  leaves.  In  greenhouses  the  disease  is 
commonly  present  but  not  in  destructive  form  as  it  is  further 
south  in  the  open.  Numerous  other  leaf-spots  also  occur  on 
the  many  varieties  of  palms. 

PANSY.    See  violet. 

PEONY 

Mold  ^^^  (Botrytis).  —  This  mold  was  first  noted  in  1897  in 
Europe.  It  has  since  been  reported  in  Canada,  Massachu- 
setts, Rhode  Island,  Pennsylvania,  and  Maryland  as  causing 
serious  loss. 

Young  plants  are  attacked  almost  as  soon  as  they  appear 
above  ground,  and  ashen  gray  spots  are  produced  upon  the 
bud-scales,  and  stems.  Among  older  plants  the  rot  develops 
upon  the  leaves,  unopened  buds,  and  at  the  base  of  the  stem. 
Brown  mold  similar  to  that  described  for  lettuce  not  in- 
frequently develops  upon   the  affected   parts.     Numerous 


Ornamental  Plaiits  429 

greenish-black,  flat  sclerotia,  1-13^  mm.  in  diameter,  are 
formed  in  the  stems. 

Dead  leaf  and  stem  remains  should  be  removed  from  the 
peonies  before  they  are  set  in  the  ground.  Bordeaux  mix- 
ture may  be  used  after  the  plants  appear  in  the  spring. 
Infested  beds  should  be  steamed.  Drop  (Sclerotinia) .  See 
lettuce. 

PETUNIA 

Drop  (Sclerotinia) .    See  lettuce. 

PHLOX 

Powdery-mildew  (Erysiphe  cichoracearum  DC).  — This  is 
of  general  distribution  and  injurious.  Leaf-spot  (Cercospora 
phlogina  Pk.). — Brown  circular  spots  occur  on  the  leaves. 

PINK 

Rust  (Puccinia  arenarice  (Schm.)  Schr.).  — This  rust  was 
described  in  1803  by  Schumacher.  It  is  quite  common  upon 
various  members  of  the  pink  family,  for  example,  chick- 
weeds,  corn  cockle,  Bouncing  Bet,  etc.  The  sori  are  large, 
raised  blisters  arranged  in  characteristic  concentric  circles. 

Diseased  plants  should  be  burned. 

PRIMROSE 

Leaf-spot  (Phyllostida  primulicola  Desm.).  —  Large,  cir- 
cular, brown,  dead  spots  are  produced  upon  the  leaves. 
Minute  dark  pycnidia  may  be  seen.  Leaf-spot  (Ascochyta 
primulce  Trail).  — Well-defined  oval  spots,  resembling  those 
of  the  phyllosticta  leaf-spot,  are  formed.  These  two  diseases 
cannot  be  distinguished  without  the  aid  of  the  microscope. 
Leaf-spot  (Ramularia  primula;  Thuem.).  —  In  this  disease 
the  blotches  are  yellow  with  centers  of  ashen  whiteness.  No 
pycnidia  are  present,  but  instead  a  gray  coating  of  mold. 
Anthracnose  (Colletotrichum  primulw  Hal.).  —  In  this  blight 


430  Diseases  of  Economic  Plants 

the  entire  leaf  is  more  often  involved  than  in  the  above 
diseases,  and  definite  spots  are  more  rare.  Dark  acervuli  are 
present. 

Gray-mold  {Botnjtis  sp.).  —  This  occurs  upon  leaves  and 
flowers  much  as  upon  lettuce. 

Bordeaux  mixture  is  useful  with  all  of  these  primrose 
diseases. 

PRIVET 

Anthracnose  ^"^  {Glomerella  cingulata,  Gloeosporium).  — 
Twig  blight  superficially  resembling  that  of  the  pear  is  a 
character  of  this  disease  in  its  later  stages,  terminal  parts  of 
the  twigs  2-5  cm.  long  being  affected.  The  line  of  separation 
between  diseased  and  healthy  tissue  is  sharp  through  shrink- 
ing and  depression  of  the  diseased  part.  In  early  stages  de- 
pressed, oblong,  diseased  spots,  at  first  very  minute,  are  seen 
upon  the  bark.  These  spots  enlarge,  eventually  girdle  the 
twig,  and  cause  the  death  of  the  distal  part.  Minute  black 
elevated  acervuli,  visible  to  the  naked  eye,  are  scattered  over 
the  surface  of  the  original  disease  spots. 

Affected  branches  should  be  cut  well  below  the  diseased 
portion  and  burned.  A  spring  spraying,  before  the  buds 
swell,  with  any  good  dormant  spray  will  still  further  reduce 
infection. 

ROSE  ^^^ 

Black-spot  ^^^  (Diplocarpon  rosce  Wolf,  Actinonema) . — 
Both  in  and  out  of  doors,  this  is  a  widely  known  and  destruc- 
tive rose  disease.  It  was  first  described  in  1824,  and  is  now 
widely  distributed  throughout  Europe  and  the  United  States. 
It  consists  of  irregular  circular  or  oval  indefinitely  bordered, 
black  spots  upon  the  upper  surface  of  leaves  that  are  mature 
or  nearly  so.  The  larger  spots  are  a  centimeter  or  more  in 
diameter,  and  they  frequently  coalesce  so  as  nearly  to  cover 
whole  leaflets. 

With  age  the  spots  turn  gray  at  the  centers,  at  which  part 


Ornamental  Plants 


431 


the  leaf  dies.  They  also  become  more  regular  in  outline  than 
in  their  earlier  stages.  Portions  of  the  leaflets  outside  of  the 
area  actually  spotted  often  turn  yellow,  and  the  diseased 
leaflets  fall  off  prematurely.  Thus  the  beds  beneath  diseased 
plants  are  often  strewn  with  fallen  leaves. 

All  infective  material  should  be  gathered  and  burned,  and 
by  use  of  a  good  dormant  spray  both  bushes  and  ground  be 


Fig.  220.  —  Rose  mildew;  diseased  and  healthy  shoots. 


well  cleared  of  superficial  spores.  Ammoniacal  copper  car- 
bonate used  once  each  week  is  effective  after  the  plants  are  in 
foliage.  Lime-sulfur  or  Bordeaux  mixture  may  be  used 
when  the  residue  on  the  foliage  is  not  objectionable. 

Powdery-mildew  {Sphceroiheca  pannosa  (Wallr.)  Lev.  or 
S.  humili  (DC.)  Burr,  Oidium.).  —  This  is  perhaps  the  most 
wide-spread  and  destructive  of  all  rose  diseases  both  under 
glass  and  in  the  open,  being  especially  destructive  to  the 


432  Diseases  of  Economic  Plants 

rambler  varieties.  In  mild  cases  it  occurs  merely  as  flour-like, 
dusty  white  patches  upon  the  leaves.  But  when  present,  it 
usually  becomes  aggressive,  attacking  the  yoUng  leaves  and 
tender  shoots,  which  become  dwarfed,  curled,  reddened,  va- 
riously deformed  (Fig.  220),  and  covered  with  the  white 
powder  of.  spores  and  spore  stalks.  The  vitality  of  the  plant 
is  so  lowered  by  repeated  attacks  and  even  by  direct  attack 
upon  the  buds  that  the  plants  become  worthless. 

Indoors  sulfur  is  serviceable.  The  house  should  be 
closed  and  the  sulfur  boiled  in  a  kettle  for  two  to  three 
hours  twice  weekly,  or  the  house  may  be  closed  in  the  morn- 
ing, the  temperature  raised  to  24°  C.  (75°  F.),  and  the  air 
well  filled  with  sulfur  from  bellows.  The  temperature 
should  then  be  raised  to  31°-32°  C.  (85°-90°  F.),  and  al- 
lowed to  cool  gradually. 

Either  out  doors  or  in,  dusting  (sulfur  90  parts,  arsenate 
of  lead  10  parts)  is  effective  and  more  convenient  than 
spraying  with  Bordeaux  mixture  or  lime-sulfur. 

Canker  ^•''''  (Cylindrocladium  scoparium  Morg.).  —  Brown, 
dead  cankers  are  formed  on  the  stems  and  branches,  or  at  the 
crown,  and  often  encircle  the  stem  for  several  centimeters. 
Consideral)le  mjury  is  done  to  roses  under  glass.  Examine 
new  stock  carefully  to  exclude  canker.  If  the  disease  enters 
the  house  remove  all  old  soil  and  disinfect  the  benches  with 
formalin.  Brown-canker  ''^^  {Diaporthe  wnbrina  Jenk., 
Phomopsis)  also  occurs  on  roses  of  many  varieties. 

Rust  (Phragmidium  subcorticum  (Schr.)  Wint.).  —  This 
true  rust  is  common  in  Europe,  and  is  found  in  many  parts 
of  the  United  States  from  the  Atlantic  to  the  Pacific;  still 
it  is  not  a  very  serious  pest. 

Early  in  the  season  orange-yellow  sori  appear  upon  the 
green  parts  of  the  plant:  on  the  leaf  as  small,  circular  spots; 
on  the  stems  and  petioles  often  as  quite  large,  powdery 
masses.  Later  in  the  season  the  color  of  the  sori  changes 
to  brick  red. 

Affected  branches  should  be  l)urned  promptly,  antl  all 
infective   material   should   be   burned   in   the   autunni.      If 


Ornamerdal  Plants  433 

the  disease  reappears,  the  whole  plant  should  be  dug  up 
and  burned.  In  beds  where  the  disease  has  occurred,  a 
dormant  spray  should  be  applied  in  early  spring.  Another 
rust  is  due  to  Earlea  speciosa  (Fr.)  Arth.  —  Though  much  like 
the  last,  this  is  limited  in  its  attack  to  the  stems,  rarely 
petioles.  The  sori  are  irregular  and  black.  Since  the  causal 
fungus  is  perennial  in  the  stems,  excision  and  burning  are  to 
be  practiced. 

Anthracnose  (Gloeospoi-imn  rosce  Hal.). — This  anthrac- 
nose  is  very  similar  to  that  of  the  raspberry.  The  diseased 
canes,  bearing  small,  pale  leaves,  die  from  the  tip  backward 
for  2-3  dm.,  and  red  acervuli  appear  upon  them  after  death. 
Often  the  canes  become  completely  defoliated. 

Affected  plants  should  be  sprayed  with  Bordeaux  mix- 
ture or  ammoniacal  copper  carbonate. 

Leaf-spot  (Mycosphcerella  rosigena  E.  &  E.).  —  The  leaves 
are  marked  with  gray,  irregular,  indefinite  blotches  which 
bear  minute  black  perithecia  in  their  centers.  Another 
leaf-spot  is  due  to  Cercospora  rosceicola  Pass.  Circular,  gray 
spots  bordered  with  dark  purple  but  without  pycnidia  are 
present. 

Downy-mildew  (Peronospora  sparsa  Berk.).  —  This  mil- 
dew is  kin  to  that  of  the  grape.  Its  spots  are  indefinite,  and 
the  characteristic,  downy,  white  to  purple  coating  is  noted 
upon  the  lower  surfaces  of  the  leaves.  It  is  not  common  in 
America.  Bronzing,  its  name  indicating  its  character, 
occurs  frequently.  It  is  not  due  to  parasites  and  does  no  real 
harm. 

Crown-gall.    See  peach. 


SEDUM 

Leaf-spot  {Septoria  sedi  West.).  —  Dark,  circular  blotches 
appear  upon  the  leaves  and  result  in  such  defoliation  that  the 
stems  often  become  naked  nearly  to  the  tips  of  the  branches. 
Infected  parts  should  be  burned.  Anthracnose  {V ermicularia 
telephii  Karst.).  — This  disease  usually  appears  first  at  the 


434  Diseases  of  Economic  Plants 

point  of  attachment  of  the  leaves,  and  later  it  passes  to  the 
stem,  causing  soft  rot  and  shrinking  of  the  outer  parts.  After 
defoliation  the  disease  spreads  slowly  toward  the  base  of  the 
stem.    Infected  parts  should  be  burned. 

SNAPDRAGON 

Anthracnose  "*■"  (Colletotrichum  antirrhini  Stew.).  —  This 
disease  which  often  ruins  the  crop  is  the  most  destructive  of 
this  host,  both  under  glass  and  in  the  open.  It  attacks  plants 
of  any  age,  producing  on  the  stem  elliptical  sunken  spots, 
5-8  mm.  long,  and  on  the  leaves  circular  dead  spots.  These 
are  at  first  dirty  white  with  narrow  brown  margins;  later 
acervuli  appear  in  the  center,  at  first  brown,  then  black. 
Diseased  plants  show  numerous,  dead,  hanging  leaves.  The 
stems  or  lateral  shoots  may  be  girdled,  killing  the  parts 
beyond. 

It  is  recommended  to  use  only  healthy  plants  for  cuttings 
and  to  clean  up  and  burn  all  diseased  refuse.  The  cuttings 
should  be  sprayed  when  well  rooted  and  repeatedly  until 
transplanted.  Excess  of  water  should  be  avoided  and 
thorough  ventilation  provided. 

Leaf-spot  '"^  (Phijllosticta  antirrhini  G.  &  A.).  —  Circular, 
brown  or  black  spots  about  one  centimeter  in  diameter, 
usually  marked  by  concentric  ridges,  appear  on  the  leaves. 
Lesions  on  the  petioles  cause  death  of  the  leaf  and  infection 
of  the  axils.  Stem  lesions  may  be  2  or  3  cm.  long  and 
eventually  girdle  the  stem,  resulting  in  death  of  all  distal 
parts.  Young  plants  die  from  typical  damping-off.  Bor- 
deaux mixture  is  recommended  for  forms  of  the  disease 
other  than  damping-off,  which  must  be  met  by  soil  dis- 
infection. 

Rust  ^''^  (Puccinia  antirrhini  D.  &  H.).  —  This  rust  has 
recently  appeared  in  greenhouses  in  destructive  form.  Dis- 
eased stock  should  be  excluded  and  sub-irrigation  adopted  if 
possible. 


Ornamental  Plants  435 


SPURGE 


Anthracnose  (Gloeosporium  euphorhice  Hal.).  —  The  attack 
usually  begins  upon  the  flower  cluster  and  passes  down  the 
stem  to  the  leaves,  which  then  fall  away,  leaving  the  naked, 
blighted  branches.  The  disease  often  interferes  seriously 
with  the  ornamental  effect  of  this  decorative  plant. 


SUNFLOWER,  JERUSALEM  ARTICHOKE 

Rust  {Puccinia  helianthi  Schw.). — ^  Both  wild  and  cul- 
tivated species  of  sunflowers  are  often  badly  rusted.  The 
early  sori  are  yellow  to  brown,  the  later  black.  Badly  rusted 
leaves  die  and  much  injury  follows  both  to  flower  and  seed. 
In  the  spring  the  cluster-cup  stage  is  sometimes  found  upon 
the  same  host.  Burning  of  infested  refuse  is  the  only  remedy 
known. 

j)j.Qp  455  (^Sclerotinia  perplexa  Law.).  —  The  disease  ap- 
pears first  in  the  root  or  lower  stem  and  spreads  upward  to 
the  heads.  It  in  general  character  resembles  lettuce  drop. 
Leaf-spot  {Septoria  helianthi-  E.  &  K.)  is  common  but  not 
serious. 

SWEET-PEA  "^4 

Anthracnose  {Glomerella  cingulata,  Gloeosporium)  occurs  as 
spots  on  stems,  leaves,  and  pods.  Seed  from  diseased  pods 
should  be  avoided. 

Powdery-mildew  (Microsphcera  al.ni,  Oidium).  —  This  is 
not  usually  troublesome  if  proper  greenhouse  conditions  are 
maintained.    See  rose. 

Streak  {Bacillus  lathyri  M.  &  T.). — Dark  streaks  occur 
on  the  stem.  Wilt  {Fusariuvi).  — See  cowpea  wilt.  Drop 
(Sclerotinia) .  —  See  lettuce.  Mosaic.  —  See  tobacco.  Root- 
rots  are  numerous,  due  to  Nematodes,  Thielavia,  Corticium, 
and  other  fungi. 


436  Diseases  of  Economic  Plants 

TULIP 

Gray-mold  (Botrytis).  —  All  parts  of  the  host  except  the 
roots  are  affected.  The  disease  was  apparently  imported 
from  Europe  and  is  now  established  throughout  the  United 
States. 

VERBENA 

Powdery-mildew  (Erysiphe  cichoracearum  DC,  Oidium). 
—  Powdery-mildew  is  quite  common  upon  verbena  under 
glass  or  in  the  open. 

The  use  of  potassium  sulphid,  1  ounce  to  3  gallons,  twice 
a  week  has  proved  effective. 

VINCA 

Rust  {Puccinia  vincm  (DC.)  Berk.)  was  apparently  im- 
ported from  Europe  and  does  occasional  damage.  Vinca 
leaf-spot  {Sphceropsis  vincce  Sacc.)  occasionally  injures  leaves 
and  stems. 

VIOLET,  PANSY 

Spot-disease  '*'^*"'  {Alternaria  vioIcb  G.  &  D.).  —  This  is  one 
of  the  widespread  and  destructive  violet  diseases.  It  attacks 
the  plant  at  any  stage  of  its  growth  and  upon  any  green  part, 
but  is  most  destructive  upon  the  foliage.  It  first  appears  as 
small,  definite,  circular,  greenish  or  yellowish- white  spots, 
varying  from  mere  dots  to  1  mm.  in  diameter.  The  light  cen- 
ter is  surrounded  by  a  narrow  ring,  usually  dark  brown  to 
black,  but  turning  lighter  with  age.  As  the  spot  enlarges  the 
freshly  diseased  tissue  is  usually  watery  and  translucent, 
and  the  center  changes  to  yellow  or  gray- white  and  may 
fall  out.  Frequently  by  the  combined  effects  of  several 
spots  the  whole  leaf  is  destroyed.  If  the  air  is  damp,  a 
thin  coating  of  rusty-colored  spores  may  be  seen  in  the  old 
spots. 

Damp,  warm,  cloudy,  summer  weather,  unclean  houses, 


Ornamental  Plants  437 

weak  plants,  poor  stock,  poor  beds,  are  predisposing  con- 
ditions to  disease. 

To  avoid  the  disease  the  houses  should  be  kept  scrupu- 
lously clean,  only  strong  stock  used,  infested  material  picked 
and  burned,  and  insects  banished.  Close  attention  must 
also  be  given  to  ventilation,  heating,  shading,  and  watering. 
The  soil  should  be  removed  each  season  and  every  means 
used  to  produce  strong  resistant  plants.  Other  leaf-spots  are 
due  to  Cercospora  violce  Sacc,  Phyllosticta  violce  Desm.  and 
Marssonina  violce  (Pass.)  Sacc.  No  pycnidia  are  present,  but 
the  centers  of  the  spots  are  darkened  by  the  presence  of 
hyphae. 

Anthracnose ''■'^  {Colletotrichum  violce-tn  col  oris  RES.). — 
This  blight  has  been  noted  in  many  states.  It  is  characterized 
by  the  appearance  of  dead,  black-bordered  spots  on  the 
leaves  and  petals,  thus  disfiguring  the  flowers,  and  affecting 
the  production  of  seed,  or  even  bringing  premature  death 
to  the  plant. 

Thorough  and  frequent  spraying  with  Bordeaux  mixture 
is  advocated. 

Wilt  "^^^  (Fusarium  violce  Wolf).  —  This  was  noted  as  of 
economic  importance  in  Nebraska,  where  it  caused  sudden 
dying  of  apparently  healthy  plants.  Slightly  sunken  areas 
were  evident  on  the  stems  just  above  the  ground,  and  the 
roots  were  reduced  to  mere  stumps. 

Rust  (Puccinia  violce  (Schm.)  DC).  —  One  of  the  most 
common  of  pansy  diseases  is  this  true  rust  which  affects  all 
aerial  parts  of  the  plant.    It  is  recognized  by  its  sori. 

Downy-mildew  (Peronospora  violce  De  Bary).  —  The 
downy-mildew  is  in  general  character  like  that  of  the  grape. 
The  spots  are  indefinite,  and  affected  plants  droop  and  die. 

Anthracnose  {Glceosporium  violce  B.  &  Br.).  —  The  an- 
thracnose  often  begins  at  the  edge  of  the  leaf,  as  an  irregular 
discoloration  which  extends  inward,  eventually  blighting  the 
whole  leaf. 

Root-rot  (Thielavia).  —  Affected  plants  are  stunted  and 
yellow.     The  underground  parts  show  numerous  dark  spots 


438 


Diseases  of  Economic  Plants 


Fig.  221.  —  Violet  leaves,  healthy  and  affected  by  spot- 
After  Dorsett. 


Ornamental  Plants  439 

of  dead  tissue  which  often  involve  the  roots  for  considerable 
distances.  The  disease  is  the  same  as  that  of  tobacco.  Root- 
rot  (Corticium),  see  p.  21. 

Mold  (Zygodesmus  albidus  E.  &  H.).  —  This  mold  forms  a 
white,  fiour-like  coat  over  the  leaf. 

VIRGINIA  CREEPER   (Ampelopsis) 

Leaf-spot  {Guignardia  hidwellii,  Phyllosticta) .  —  The  spots 
occurring  upon  the  leaves  and  shoots  are  identical  in  ap- 
pearance with  those  upon  the  grape,  and  the  same  treatment 
is  recommended. 

Powdery-mildew.    See  grape. 

Stem-rot  {Cladosporium  herbarum  Lk.).  —  Large  blanches 
or  even  the  entire  plant  may  be  killed. 

WATER-LILY 

Leaf-spot  (Cercospora).  —  Circular  spots,  at  first  pale 
green,  later  yellow,  and  finally  Ijrown  and  dead,  are  produced 
upon  the  leaves.  The  dead  tissue  may  break  away,  leaving 
irregular  holes. 

Soda-Bordeaux  mixture  is  recommended,  since  it  is  effec- 
tive and  does  not  spot  the  leaves.  It  is  beneficial  also  in 
removing  undesired  algal  growth.  Another  leaf-spot  is  due 
to  Helicosporium  nymphcearum  Rand.  —  Dark  spots  often 
red-bordered  occur  on  the  leaves  and  may  enlarge  to  involve 
the  whole  leaf. 


FUNGICIDES  * 

Bordeaux  mixture.  ''■>'•  '''•  ''■'''•  ''•'^'  ''^  —  The  4-4-50  fonuula 
(4  pounds  of  copper  sulfate  crystals  and  4  pounds  of  stone- 
lime  to  50  gallons  of  water)  is  one  in  conunon  use. 

According  to  the  common  formulas  several  times  as  much 
lime  is  used  as  is  necessary  to  precipitate  the  copper.  A 
mixture  used  abroad,  known  as  the  Woburn  mixture,  calls  for 
a  solution  of  copper  sulfate  with  lime  water  and  subsequent 
dilution  as  contrasted  with  milk-of-lime  used  in  the  ordinary 
Bordeaux  mixture.  According  to  Pickering  ordinaiy  Bor- 
deaux mixture  and  the  Woburn  mixture,  containing  only 
one-sixth  as  much  copper,  seem  to  be  equivalent  in  fungicidal 
action. 

To  make  large  quantities  of  Bordeaux  mixture,  or  small 
amounts  repeatedly,  it  is  desirable  to  prepare  separate  con- 
centrated stock  solutions  of  copper  sulfate  and  of  lime. 
These  are  made  up  at  the  rate  of  approximately  one  pound 
of  each  to  the  gallon.  In  preparing  a  stock  solution  of 
copper  sulfate,  a  weighed  amount  of  the  commercial  crystals, 
"bluestone,"  is  placed  in  a  sack  and  suspended  in  water  in  a 
barrel  or  other  wooden  vessel.  The  volume  of  the  water 
should  equal  in  gallons  the  weight  of  the  copper  sulfate  in 
pounds.  The  solution,  as  formed,  will  flow  to  the  bottom, 
leaving  comparatively  fresh  water  in  contact  with  the  re- 
maining crystals.  Stirring  partially  defeats  the  purpose  of 
this  method  by  increasing  the  concentration  of  copper 
sulfate  in  the  liquid  in  contact  with  the  undissolved  part. 
If  the  copper  sulfate  is  placed  in  the  bottom  of  the  barrel,  it 
will  dissolve  but  slowly  even  with  frequent  stirring.  When 
dissolved,  the  solution  should  be  made  uniform  by  stirring. 

In  preparing  the  stock  solution  of  lime  (the  term  in  com- 
*  Prepared  by  W.  A.  Ruth. 
440 


Fungicides 


441 


mon  use  in  this  connection  for  a  suspension  of  calcium  hy- 
droxid)  a  definite  quantity  of  fresh  stone-hme  is  placed  in  a 
trough,  slaked,  and  made  up  to  a  volume  corresponding  in 
gallons  to  the  weight  of  the  lime  in  pounds.  In  slaking  the 
lime  a  small  quantity  of  water  is  used  to  start  the  reaction, 
and  just  enough  water  is  added,  as  the  lime  slakes,  to  prevent 
crumbling.  The  lime  and  water  are  stirred  from  the  time  the 
hme  starts  to  slake  until  the  reaction  appears  to  be  complete. 


Fig.  222.  —  A   convenient    arrangement    for    mixiiif",    Bordeaux 
mixture.     After  Vermont  Agr.  Exp.  Sta. 

Instead  of  diluting  to  the  final  volume  at  this  point,  it  is 
somewhat  desirable  to  add  just  enough  water  to  prevent 
drying  out  and  to  allow  the  mixture  to  cool  before  the  further 
addition  of  water.  This  procedure  permits  further  slaking, 
which  results  in  a  noticeably  creamier  stock  solution,  with 
fewer  particles  of  unslaked  lime  to  clog  the  nozzles. 

The  common  method  in  use  in  making  Bordeaux  mixture 
in  the  field  has  been  to  dilute  the  required  quantities  of 
copper  sulfate  and  lime  separately  to  half  the  final  volume 


442  Diseases  of  Economic  Plants 

required  and  to  pour  them  together  into  a  separate  con- 
tainer, usually  the  tank  of  the  sprayer.  The  colloidal  sus- 
pension obtained  by  this  method  of  mixing  settles  very 
slowly  and  can  be  applied  with  the  maximum  uniformity. 
To  make  200  gallons,  the  content  of  the  usual  power  sprayer, 
by  this  method,  an  elevated  platform,  or  a  series  of  elevated 
platforms,  is  required.  The  diluted  lime  and  copper  sulfate 
are  run  simultaneously  from  100-gallon  wooden  contain- 
ers standing  on  the  platform  into  the  sprayer,  or  into  an 
elevated  200-gallon  tank,  where  the  resulting  Bordeaux 
mixture  is  held  in  readiness  to  supply  the  power  sprayer 
while  the  smaller  containers  are  being  refilled. 

The  above  method  is  open  to  improvement  because  of  the 
large  amount  of  apparatus  and  labor  involved. 

Hawkins  claims  "a  Bordeaux  mixture  in  which  the  sus- 
pension of  the  copper  compound  settles  out  slowly  may 
be  prepared  by  adding  the  concentrated  calcium  hydroxid 
to  the  diluted  copper  sulfate  solution  or  vice  versa,  pro- 
vided the  mixture  is  sufficiently  agitated."  He  states  that 
"the  agitation  necessary  for  preparing  Bordeaux  mixture 
with  a  low  rate  of  subsidence  by  this  method  could  hardly  be 
obtained  in  practice  except  by  means  of  a  power  outfit  pro- 
vided with  a  good  agitator."  This  method  can  be  used  to 
advantage  with  the  tank-filler,  a  jet  pump,  with  which 
any  power  sprayer  can  be  equipped,  which  permits  the  rapid 
filling  of  the  spray  tank  by  means  of  the  spray  pump.  The 
construction  of  a  platform  and  the  expense  of  pumping  water 
into  the  elevated  containers  are  thereby  obviated.  Sixteen 
gallons  of  stock  copper  sulfate  or  lime  is  first  diluted  in  the 
spray  tank  to  within  sixteen  gallons  of  the  final  volume,  the 
stock  solution  of  the  other  component  is  poured  in,  and  the 
mixture  is  thoroughly  agitated.  A  method  very  similar  to 
this  has  proved  satisfactory  in  the  field  and  is  in  common  use 
in  Illinois. 

Wooden  containers  should  always  be  used  for  the  copper 
sulfate  solutions,  and  the  lime  or  Bordeaux  mixture  should 
always  be  strained  before  it  enters  the  tank. 


Fungicides  443 

Lime-sulfur. ^^^  —  This  fungicide  (the  material  is  also 
used  in  the  control  of  San  Jose  scale)  is  prepared  by  boiling, 
in  water,  lime  and  sulfur  in  the  proportion  of  approximately 
two  parts  of  sulfur  to  one  of  lime.  The  products  in  the 
resulting  solution  are  calcium  thiosulfate  (CaSoOs),  calcium 
tetrasulfid  (CaSi),  and  calcium  pentasulfid  (CaSs).  The 
material  may  be  made  by  the  orchardist  or  bought  from 
manufacturers.  The  commercial  product  is  more  concen- 
trated than  that  made  by  the  formulas  usually  recom- 
mended for  home  use,  and  contains  a  higher  proportion 
of  polysulfid  sulfur  (that  is,  sulfur  in  the  form  of  CaS4 
and  CaSa). 

The  combination  of  constituents  ^^^  that  appears  best  to 
meet  the  largest  number  of  desirable  conditions  is  the  follow- 
ing, stated  in  round  numbers: 

36  pounds  of  lime  (pure  lime,  CaO,  used  as  a  basis). 
80  pounds  of  high  grade,  finely  divided  sulfur. 
50  gallons  of  water. 

When  lime  containing  impurities  is  used,  more  than  36 
pounds  must  be  taken  in  order  to  obtain  36  pounds  of  pure 
lime. 

Use  38  pounds  of  lime  containing  5  per  cent  of  impurities 
(95  per  cent  pure). 

Use  40  pounds  of  lime  containing  10  per  cent  impurities 
(90  per  cent  pure). 

No  lime  should  be  used  which  contains  more  than  10  per 
cent  of  impurities.  If  the  lime  contains  impurities  (oxid  of 
magnesium,  iron,  aluminum,  etc.,  and  carbonates  of  mag- 
nesium, calcium,  etc.),  these  do  not  go  into  solution  but  re- 
main as  sediment,  together  with  any  undissolved  sulfur 
not  acted  upon  because  of  insufficiency  of  pure  lime,  due  to 
impurities  in  the  lime  used.  The  amount  of  sediment  thus 
formed  can  be  utilized  as  a  measure  of  the  amount  of  im- 
purities existing  in  the  lime. 

The  level  of  the  mixture  during  l^oiling  should  be  kept  near 
the  50-gallon  mark  —  not  being  allowed  to  drop  more  than  an 


444  Diseases  of  Economic  Plants 

inch  below  —  this  regulation  is  accomplished  by  adding  water 
from  time  to  time  in  the  required  amounts.  It  is  preferable  to 
add  water  in  small  amounts  at  frequent  intervals  rather  than 
larger  amounts  less  often,  since  the  boiling  is  less  interrupted. 
When  the  boiling  is  completed,  the  level  of  the  liquid  should 
be  made  up  to  the  50-gallon  mark,  if  not  already  there. 
It  will  be  found  to  have  a  density  of  24°  to  25°  Bamne  when 
cooled  to  about  16°  C.  (60°  F.). 

One  gallon  of  this  solution  may  be  diluted  with  25  gallons 
of  water  for  summer  use  as  a  fungicide.  Commercial  solu- 
tions, which  usually  test  about  33°  Baume,  may  be  diluted 
with  40  parts  of  water.  The  degree  of  dilution  has  relatively 
slight  effect,  however,  upon  the  fungicidal  properties  of  the 
solution,  in  comparison  with  the  effect  of  thoroughness  of 
application,  and  the  amount  of  dilution  may  vary  within 
wide  limits. 

Another  method  for  making  lime-sulfur  consists  in  the 
use  of  live  steam,  furnished  by  a  boiler,  and  led  into  wooden 
barrels  or  tubs,  in  which  the  mixture  is  boiled  (Fig.  223). 
Large  tubs  provided  with  mechanical  agitators  are  sometimes 
used.  Less  water  is  needed  than  is  called  for  by  the  formula 
given  above,  because  of  the  condensation  of  the  steam  used  in 
heating. 

Self-boiled  lime-sulfur  wash.  —  The  self-boiled  lime- 
sulfur  wash  is  a  combination  of  lime  and  sulfur  boiled 
with  only  the  heat  of  the  slaking  lime,  and  is  primarily  in- 
tended for  summer  spraying  of  peaches.  Peach  foliage  is  so 
susceptible  to  spray  injury  that  ordinary  Bordeaux  mixture 
cannot  be  used  as  a  summer  spray;  neither  can  the  sulfur 
washes  which  contain  any  considerable  quantity  of  sulfids 
in  solution.  The  self-boiled  lime-sulfur  wash,  however, 
when  prepared  as  a  mechanical  mixture  of  lime  and  sulfur 
with  only  a  small  percentage  of  the  sulfur  in  solution,  is  not 
injurious  to  peach  foliage  and  has  proved  to  be  a  good  fun- 
gicide. 

The  mixture  that  appears  to  be  the  most  satisfactory  is 
composed  of 


Fungicides  445 

Lime 8  pounds 

Sulfur 8  pounds 

Water 50  gallons 

This  can  best  be  prepared  in  rather  large  quantities  — 
16  pounds,  or  even  32  pounds  at  a  time  —  so  as  to  get  enough 
heat  to  produce  a  violent  boiling  for  a  few  minutes.    Place  the 


223.  —  Making  lime-sulfur  wash.    After  Sherman. 


lime  in  a  barrel  and  pour  on  enough  water  (about  3  gallons  to 
16  pounds)  to  start  it  slaking  and  to  keep  the  sulfur  off  the 
bottom  of  the  barrel.  Then  add  the  sulfur,  which  should 
first  be  worked  through  a  sieve  .to  break  up  the  lumps,  and 
finally  enough  water  to  slake  the  lime  into  a  paste.  Con- 
siderable stirring  is  necessary  to  prevent  caking  on  the  bot- 
tom. After  the  violent  boiling  which  accompanies  the  slaking 
of  the  lime  is  over,  the  mixture  should  be  diluted  ready  for 
use,  or  at  least  enough  cold  water  added  to  stop  the  cooking; 


446  Diseases  of  Econornic  Plants 

5  to  15  minutes,  according  to  whether  the  Hme  is  quick-acting 
or  sluggish,  are  required  for  the  process.  At  the  end  of  30 
or  40  minutes,  if  the  hot  mass  is  permitted  to  stand  undiluted 
as  a  thick  paste,  a  liquid  is  produced  that  is  dangerous  to 
peach  foliage  and  in  some  cases  even  to  apple  foliage. 

The  mixture  should  be  strained  through  a  sieve  of  20 
meshes  to  the  inch  in  order  to  remove  the  coarse  particles 
of  lime,  but  all  the  sulfur  should  be  worked  through  the 
strainer. 

Hot  water  may  be  used  to  good  advantage  in  preparing 
the  mixture  with  sluggish  lime,  but  with  quick-acting  lime 
hot  water  is  not  best.  The  mixture  may  be  kept  for  a  week 
or  more  without  deterioration,  but  it  should  be  thoroughly 
stirred  before  using. 

In  applying  the  self-boiled  lime-sulfur  wash  the  spray- 
ing outfit  should  be  equipped  with  a  good  agitator.  The 
agitator  of  the  ordinary  barrel  sprayer  is  not  usually  ade- 
quate. 

Sulfur-dust.'^'*^'  ■'°-'  ■''^"'-  ^°'''  ^^-  —  Very  favorable  reports  have 
appeared  recently  of  the  results  secured  by  the  use  of  sulfur 
dust  as  a  fungicide  for  apple  scab  in  New  York.  Results 
obtained  by  experiments  carried  on  further  south  have  not 
been  favorable  to  its  use  for  this  purpose.  Thus  Giddings 
states  that  as  the  result  of  four  years'  trial  it  can  not  be 
recommended  for  use  on  apples  where  scab  or  sooty  blotch  is 
severe,  or  for  the  treatment  of  bitter-rot,  black-rot,  or  blotch. 
Brock  finds  in  Illinois  that  spraying  is  much  superior  to 
dusting  for  the  control  of  fungi,  but  believes  that  in  favored 
localities,  where  fungi  are  comparatively  easy  to  control,  the 
sulfur  dust  has  its  uses. 

Reddick  and  Crosby  recommend,  for  the  average  Western 
New  York  conditions,  a  mixture  containing  85  per  cent  of 
exceedingly  finely  ground  sulfur  (especially  ground,  "super- 
fine") and  15  per  cent  of  dry  arsenate  of  lead  (the  "fluffy" 
sort  is  used  for  this  purpose).  The  exact  quantity  of  mate- 
rial to  be  used  per  tree  will  be  determined  by  the  wind, 
the  size  and  the  shape  of  the  trees,  and  also  by  the  thorough- 


Fungicides  447 

ness  of  distribution  effected.  From  1.25  to  2.5  pounds  are  ap- 
plied per  tree  in  each  application.  '*  In  localities  where  apple 
scab  is  less  abundant  than  in  the  lake  counties,  as  seems  to  be 
the  case  in  most  of  the  Hudson  River  section,  the  quantity  of 
sulfur  applied  per  tree  may  be  reduced.  It  would  be  well, 
however,  to  regard  these  as  minimum  amounts  until  expe- 
rience has  shown  that  they  can  be  reduced  with  safety." 

Dusting  appears  to  be  slightly  more  expensive  than  spray- 
ing. The  cost  of  materials  is  higher,  but  this  factor  in  the 
total  cost  is  partially  overcome  by  the  lower  cost  of  applica- 
tion. The  chief  advantage  in  dusting,  however,  lies  in  the 
extreme  rapidity  with  which  the  dust  can  be  applied.  This 
appears  to  permit  the  application  of  the  fungicide  at  periods 
when  the  weather  conditions  favor  infection  with  apple  scab, 
and  to  result  in  comparative  flexibility  in  the  spray  schedule. 

Ammoniacal  solution  of  copper  carbonate.  —  This  solution 
contains  no  sediment,  and  on  drying  leaves  no  unsightly 
marks.  It  may  therefore  be  used  when  the  spotting  that 
the  Bordeaux  mixture  causes  precludes  the  use  of  that 
fungicide.  The  mixture  consists  of  a  solution  made  by  dis- 
solving copper  carbonate  in  ammonia-water  in  the  following 
proportions : 

Copper  carbonate 6  ounces 

Ammonia,  about 3      pints 

Water 50  gallons 

Weigh  out  the  proper  amount  of  copper  carbonate.  Set  a 
very  small  portion  of  this  aside,  and  dissolve  the  remainder 
of  it  in  diluted  ammonia,  using  only  enough  ammonia  to 
dissolve  it.  Then  add  the  portion  of  copper  carbonate  which 
was  reserved.  This  will  insure  the  use  of  no  more  ammonia 
than  is  necessary.  It  is  better  to  have  a  little  too  much  of 
the  carbonate  in  the  solution  than  to  have  too  much  ammonia. 
The  strong  solution  made  in  this  way  can  be  diluted  with  the 
proper  amount  of  water.  The  copper  carbonate  may  be 
purchased  directly  from  the  drug-store,  or  it  may  be  prepared 
at  home. 


448  Diseases  of  Economic  Plants 

To  make  copper  carbonate  proceed  as  follows:  Dissoh^e 
10  pounds  of  copper  sulfate  in  10  gallons  of  water.  Also 
dissolve  12  pounds  of  carbonate  of  soda  in  the  same  amount  of 
water.  Allow  these  two  solutions  to  cool,  then  mix  them 
slowly  together,  stirring  in  the  meantime.  Allow  the  mixture 
to  settle  about  12  hours,  pour  off  the  liquid,  and  add  water 
equal  in  amount  to  the  liquid  poured  off.  Stir  thoroughly 
and  allow  it  to  settle  as  before.  Repeat  this  operation  again, 
then  drain  off  all  the  liquid  possible,  and  dry  the  blue  powder 
which  remains.     This  powder  is  the  copper  carbonate. 

Burgundy  mixture. 

Copper  sulfate 2  pounds 

Sodium  carbonate  (sal  soda) 3  pounds 

Water 100  gallons 

Each  chemical  should  be  dissolved  separately  in  half 
the  water,  then  mixed  as  in  making  Bordeaux  mixture. 
This  mixture  may  be  used,  as  may  ammoniacal  copper 
carbonate,  when  it  is  advisable  to  avoid  the  spotting  of 
fruit  which  would  result  from  use  of  the  Bordeaux  mixture. 

Copper  sulfate  solution,  1-17.  —  A  solution  consisting 
merely  of  copper  sulfate  and  water  to  kill  spores  on  the 
bark  and  supports  may  be  used  before  the  leaves  appear. 

Dissolve  the  copper  sulfate  as  in  preparing  the  Bordeaux 
mixture,  dilute  it  to  the  required  strength,  and  spray  upon  the 
trees.  The  addition  of  a  little  lime,  one  half  pound  to  50 
gallons  of  mixture,  enables  the  operator  to  see  exactly  what 
portions  of  the  tree  have  been  sprayed. 

This  mixture  must  not  be  used  after  the  leaves  appear. 

Potassium  sulfid  solution. 

Potassium  sulfid  (liver  of  sulfur) 1  ounce 

Water 2  to  4  gallons 

This  solution  should  be  freshly  prepared.  It  is  used  as  a 
substitute  for  the  Bordeaux  mixture,  to  avoid  spotting,  in 


Fungicides  449 

the  same  way  that  the  ammoniacal  sohition  of  copper  car- 
l)onate  is  used.  Potassium  sulfid  is  also  especially  efficient 
as  a  protection  against  the  powdery-mildews. 

Formalin.  —  Formalin  is  a  very  powerful  germicide  which 
came  into  wide  use  about  1889.  Its  interest  to  the  farmer 
lies  chiefly  in  its  power  to  prevent  the  potato  scab,  onion 
smut,  and  the  various  smuts  of  cereals.  Full  directions  for 
its  use  are  given  under  special  crops. 

This  substance  appears  on  the  market  under  two  names: 
"Formalin"  and  "37  per  cent  formaldehyde."  These  sub- 
stances are  absolutely  identical,  and  since  the  formaldehyde 
solution  is  cheaper,  owing  to  the  fact  that  the  word  "For- 
malin" is  protected  by  patent,  the  customer  will  of  course  do 
well  to  purchase  the  37  per  cent  solution. 

Corrosive  sublimate. 

Corrosive  sublimate 1    part 

Hj'drochloric  acid 2  parts 

Water 1000  parts 

This  is  employed  chiefly  as  a  seed  disinfectant  particu- 
larly for  black-rot  of  cabbage.  It  is  intensely  poisonous 
and  should  be  so  regarded. 

Flowers  of  sulfur.  —  This  substance  is  chiefly  employed 
as  a  specific  for  the  powdery-mildews.    See  grape,  p.  122. 

Proprietary  fungicides. ^^^  —  There  are  several  proprie- 
tary fungicides  on  the  market.  Of  five  tested  on  apples 
in  1916,  at  the  Illinois  Experiment  Station,  four  produced 
serious  foliage  injury  and  more  or  less  serious  injury  to  fruit. 
There  are  several  commercial  Bordeaux  pastes  on  the  market. 
Wallace  has  shown  that  none  which  he  tested  remains  in 
suspension  as  well  as  fresh  home-made  Bordeaux  mixture 
(some  are  very  poor  in  this  respect)  and  that  they  are  very 
expensive  if  diluted  to  contain  a  copper  content  equal  to  that 
of  4-4-50  Bordeaux  mixture. 

Combined  fungicide  and  insecticide.  —  When  an  insecti- 
cide and  a  fungicide  are  to  be  used  at  the  same  time,  it  is 


450  Diseases  of  Economic  Plants 

usually  possible  to  combine  the  two  so  that  only  one  applica- 
tion is  necessary.  The  stomach  poison  which  is  commonly 
used  for  spraying  tree  fruits  is  lead-arsenate.  It  comes  in  two 
forms,  the  powder  and  the  paste.  The  latter  contains  50  per 
cent  of  water.  The  powder  should  be  the  fluffy,  finely  di- 
vided kind.  Either  form  may  be  used  with  Bordeaux  mix- 
ture or  boiled  or  self-boiled  lime-sulfur.  The  powder  is  vised 
at  the  rate  of  1  pound  to  50  gallons  of  spray,  the  paste  at 
the  rate  of  2  pounds  to  50  gallons. 

Paris  green  can  not  be  used  with  lime-sulfur,  at  least  in 
spraying  tree  fruits,  because  of  the  resulting  foliage  and  fruit 
injury.  When  used  with  Bordeaux  mixture  for  spraying 
other  plants  it  may  be  made  up  at  the  rate  of  5  ounces  to 
each  50  gallons  of  spray. 

Calcium  arsenate  seems  to  be  a  promising  stomach  poison 
for  use  with  Bordeaux  mixture  or  lime-sulfur. 

Nicotine  preparations  for  the  control  of  plant  lice  can  be 
used  with  lime-sulfur,  or  with  lime-sulfur  and  lead  arsenate. 
There  have  been  reports  indicating  that  it  should  not  be  used 
with  Bordeaux  mixture. 

Bordeaux  injury.  •'^^'  ^^"'  ^^^  —  Many  plants  sprayed  with 
Bordeaux  mixture  assume  a  deeper  color  and  are  more 
vigorous  and  live  longer  than  unsprayed  plants,  even  in  the 
absence  of  fungous  attacks.  The  potato  is  a  notable  exam- 
ple. Other  plants  are  injured  to  a  greater  or  less  extent.  The 
peach,  plum,  sweet  cherry,  and  apricot  are  so  severely  af- 
fected by  Bordeaux  mixture  that  this  fungicide  is  not  used  in 
spraying  them. 

Ever  since  the  first  trials  of  Bordeaux  mixture  upon  the 
apple,  some  injury  has  been  noted  upon  both  leaves  and 
fruit,  due  to  the  mixture  itself.  The  amount  of  injury  differs 
with  different  varieties  and  with  other  conditions.  Water, 
deposited  as  rain  or  dew  on  the  surface  to  which  Bordeaux 
mixture  has  been  applied,  is  a  necessary  contributing  cause. 
As  the  season  advances  the  foliage  becomes  more  susceptible. 
On  the  other  hand,  the  fruit  is  most  susceptible  early  in  the 
season.    The  most  damage  to  the  fruit  occurs  from  the  spray 


Fungicides  451 

applied  just  after  the  petals  have  fallen,  and  even  the  most 
susceptible  varieties  become  almost  completely  immune 
within  a  period  of  six  or  ten  weeks  after  this  stage. 

On  the  fruit,  injury  is  manifested  by  the  formation  of  small 
black  specks  or  the  surface  is  russeted,  sometimes  very 
severely,  and  the  fruit  may  be  split  or  otherwise  distorted. 
Injury  to  the  foliage  may  first  appear  a  few  days  after  spray- 
ing or  may  be  delayed  for  several  weeks.  Brown,  dead  spots 
are  frequently  caused,  which  may  be  followed  by  the  yellow- 
ing and  falling  of  the  leaf.  Yellowing  may  occur,  however, 
when  no  brown  spotting  is  observed. 

Before  the  discovery  of  the  fungicidal  properties  of  lime- 
sulfur  and  its  efficiency  as  an  early  summer  spray,  various 
methods  were  suggested  for  the  mitigation  of  Bordeaux  in- 
jury. At  present,  lime-sulfur  has  very  largely  replaced 
Bordeaux  mixture  for  use  in  the  early  summer. 

There  are,  however,  circumstances  under  which  Bordeaux 
mixture  is  still  used  at  this  season.  It  is  generally  conceded 
that  lime-sulfur,  applied  with  sufficient  frequency,  gives  as 
good  control  of  apple-scab  as  Bordeaux  mixture,  but  that  it 
is  less  adhesive  and  must  be  applied  more  frequently.  Since 
the  period  when  the  trees  are  in  blossom  is  sometimes  pro- 
longed by  adverse  weather  conditions,  Bordeaux  mixture  is 
still  consistently  used  by  some  fruit  growers  for  the  pre- 
bloom  spray,  on  varieties  locally  subject  to  severe  injury  from 
scab.  Bordeaux  mixture  may  be  used  for  the  early  blotch 
sprays  on  varieties  not  subject  to  Bordeaux  injury,  for  all 
varieties  in  the  control  of  bitter-rot  and  blotch  after  the 
period  of  immunity  to  serious  Bordeaux  injury  has  been 
attained,  and  of  course  for  the  entire  program  for  varieties 
immune  to  this  form  of  injury. 

Hedrick  ^^^  has  published  an  extensive  list  of  apples  classi- 
fied as  to  their  immunity  or  susceptibility  to  Bordeaux  in- 
jury. 

Lime-sulfur  injury,  ^i^  '^^'^  —  Lime-sulfur  injures  many 
plants  very  seriously.  Slight  injury  to  the  leaves  of  apples  is 
of  common  occurrence.    It  is  not  usually  of  great  consequence 


452  Diseases  of  Economic  Plants 

or  of  a  lasting  nature.  The  injury  consists  of  irregular  brown 
spotting,  especially  where  the  spray  accumulates  immediately 
after  its  application.  If,  however,  the  leaves  have  been 
injured  by  apple-scab,  previous  to  the  application  of  the 
spray,  the  damage  done  to  the  foliage  is  very  serious.  There 
is  no  marked  degree  of  varietal  susceptibility  with  apples. 
The  injury  occurs  soon  after  the  spray  has  been  applied,  not, 
as  in  the  case  of  Bordeaux  injury,  at  a  period  which  may  be 
long  after  its  application.  The  foliage  is  least  susceptible  to 
injury  soon  after  it  has  unfolded.  Talbert  states  that  the 
dormant  spray  consisting  of  commercial  lime-sulfur,  testing 
33°  Baume,  may  be  applied  to  apple  trees  diluted  1  to  7  or 
1  to  8  after  growth  starts  and  until  the  trees  begin  to  bloom, 
without  material  injury  to  the  leaves  or  flower  buds. 
This  is  a  much  higher  concentration  than  is  usually  used 
when  the  trees  are  in  foliage. 

Lime-sulfur  injury  to  the  fruit  occurs  occasionally,  as  the 
result  of  drenching.  It  is  generally  conceded  that  injury 
to  the  fruit  occurs  if  lime-sulfur  is  used  in  hot  weather, 
after  the  fruit  has  developed  to  approximately  the  size  at 
which  it  becomes  relatively  immune  to  Bordeaux  injury. 
From  this  stage  onward,  Bordeaux  mixture  is  again  used, 
regardless  of  the  foliage  injury  produced.  Lime-sulfur  injury 
may,  however,  result  from  the  application  made  just  after 
the  petals  fall  or  those  just  following. 


Spraying  Apparatus 

Whether  for  spraying  a  small  garden  or  a  large  commercial 
orchard  proper  apparatus  is  needed. 

The  chief  types  of  pumps  are  briefly  mentioned  be- 
low. 

Bucket  pumps.  —  These  pumps  are  suited  for  use  in  the 
garden;  to  spray  the  bushes  or  a  few  small  fruit  trees  in  the 
yard.  The  fact  that  they  may  be  used  in  any  ordinary 
bucket  or  pail  gives  them  an  advantage  over  some  of  the 
other  outfits.     By  the  attachment  of  a  foot  rest  which  ex- 


Fungicides  453 

tends  outside  the  pail  to  the  ground,  the  pump  can  be  held 
firmly. 

Compressed  air  sprayer.  —  After  the  tank  is  partly 
filled  with  the  spray  mixture  and  closed,  air  is  pumped 
in,    thus   pressure   is   exerted    upon    the   liquid,    which    is 


Fu;.  224.  —  Bucket  pump 
showing     hose,     nozzle, 
and  bucket  attachment.      Fifi.  225.     -  Barrel  jtumi)  showing  agitator. 
After  Gould  Mfg.  Co.  After  Gould  Mfg.  Co. 

forced   out  in  the  form  of  a  fine   spray  when  the  nozzle 
is  opened. 

This  type  of  sprayer  is  satisfactory  in  some  instances, 
and  is  adapted  to  about  the  same  fields  as  the  bucket 
pump.  It  is  not  well  adapted  for  spraying  large  areas, 
since  the  sprayers  are  inconvenient  to  carry,  are  slow  and 
heavy. 


454 


Diseases  of  Economic  Plants 


Knapsack  sprayers.  —  These  consist  of  3  to  5-gallon 
tanks,  with  straps  so  attached  that  the  outfit  can  be  car- 
ried upon  the  back  in  the  manner  of  a  knapsack.  The 
handle  is  so  adjusted  that  it  is  operated  in  front  of  the 
carrier.  These  pumps  are  best  adapted  to  spraying  crops 
which  grow  breast  high,  as  grapes.  They  may  also  be 
used    in    spraying   small   trees.     For  general   garden  use. 


Fig.  226.  —  Modern  power  sprayer,  equipped  with  high-pressure, 
slow-speed  pump,  with  large  bearings,  ball  valves,  modern  pressure 
regulator,  etc.  Such  a  machine  is  constructed  to  turn  in  a  small 
space.  A  tower  can  be  set  on  the  tank  for  spraying  tall  trees  with 
extension  rods. 


or  small  areas,  a  half  acre  to  an  acre,  they  are  to  be 
recommended. 

Barrel  pump.  —  For  home  orchard  work  the  barrel  sprayer 
is  of  most  importance.  The  pump  is  adjusted  to  a 
barrel,  at  either  the  side  or  end.  It  should  be  provided 
with  a  good  agitator  to  keep  the  spraying  mixture  stirred 
while  in   use. 

Field  sprayers.  —  This  sort  of  sprayer  is  used  in  spray- 


Fungicides 


455 


Fig,  227.  —  The  power  sprayer  in  use  for  spraying  orchard  trees. 


456 


Diseases  of  Economic  Plants 


used  in  shade 


Fig.  227.  Smaller  ma- 
chines differ  essen- 
tially only  in  capacity. 

The  adaptation  of 
such  outfits  to  various 
purposes  is  shown  in 
Figs.  228,  229. 

The  Spray  Gun. — 
A  recent  development 
in  power  spraying  is 
the  spray  gun.  By 
its  use  one  man   can 


ing  low  plants,  such  as 
strawberries,  potatoes, 
tomatoes,  cabbage, 
etc.  Several  nozzles 
are  attached  and 
several  rows  can  be 
treated  at  one  time. 
Where  a  number  of 
acres  of  truck  crops  are 
grown,  this  sprayer  is 
of  great  advantage. 

Power  sprayers.  — 
For  operating  commer- 
cial orchards,  power 
sprayers  are  a  neces- 
sity, and  are  almost 
necessary  for  large 
home  orchards,  con- 
sisting, for  example, 
of  50  or  60  large  ap- 
ple trees.  A  modern 
power  sprayer  for  use 
in  large  orchards  is 
illustrated  in  Fig.  226, 
a   still    larger    one   in 


^mma^m 

_.  *mm 

.J^mI 

Fig.    229,  —  Power   sprayer   adapted   to 
spraying  beans. 


Fungicides 


457 


Sr.'-^^,'^ 

.k*t; 

'M 

v^- 

'  :h 

A 

^^^*' 

-t' 

''            '^i-i 

^\- 

. 

M 

u  \^m 

.fl 

.--,^ 

Fig.  230.  —  The  nozzles  are  turned  v,l  m\  aiiu,lu  to  the  lui 

spray  may  be  directed  upward  or  downward.    After  Faurot, 


uiL  the 


rapidly  spray  even  the  tallest  fruit  tree,  a  special  device  en- 
abling the  operator  to  throw  the  spray  to  different  distances. 
Spray  gims  are  being  used  by  many  commercial  growers. 

Conveyors.  —  To  economize  still  further  in  time  and  labor, 
conveyors  are  used  in  many  commercial  orchards.  These 
are  400-gallon  tanks  equipped  with  low-pressure,  high-speed 
pumps,  and  gasoline 
engines.  The  conveyor 
carries  the  spray  from 
the  mixing  plant  to 
the  sprayer.  Two  hun- 
dred gallons  of  spray- 
ing material  can  Ije 
transferred  from  the 
tank  of  the  conveyor 
to  that  of  the  sprayer 
in  less  than  two  min- 
utes. In  this  way  the 
power  sprayer  is  kept  Fig.  231.  —  Spraying  grapes. 


458 


Diseases  of  Economic  Plants 


running  almost  continuously,  thus  sometimes  doubling  its 

output. 

The  use  of  extension  rods  and  the  tower  in  spraying  is 

shown  in  Fig.  230. 

Nozzles.'"'*^— The  va- 
rious types  of  nozzles 
are  illustrated  in  Fig. 
234.  These  include 
the  Bordeaux  type 
(upper  left  corner) ,  the 
Vermorel    (lower    left 


Fig.  232.  —  Spraying  apparatus. 


corner) ,  and  the  eddy-chamber  type. 
The  last  is  the  best  type  of  nozzle 
for  spraying,  and  many  forms  of 
it  are  on  the  market.  The  eddy- 
chamber  angle  nozzle  (lower  right- 
hand  corner)  is  a  comparatively  re- 
cent development. 


ftw 

t 

i     * 

4^ 

^ 

Fig.  234.  —  Various  types  of  nozzles. 


Fig.  233.  —  Diagram  of 
longitudinal  section  of 
a  spray  nozzle  showing 
all  the  parts  that  may 
be  found  in  the  eddy- 
chamber  nozzles.  O,  ori- 
fice; EC,  eddy-chamber; 
P,  post  on  the  direct- 
ing disc,  DD;  C,  Cap; 
W,  washer;  OB,  oblique 
supply  holes;  S,  strainer; 
R,  reservoir;  B,  base  of 
nozzle;  D,  disc,  C,  cen- 
tral supply  hole.  After 
Crane. 


Dusting  machines.  —  These  consist  of  various  forms  of 
blowers  driven  by  hand  or  by  gasoline  engines.  Fig.  235 
shows  one  of  these  machines  in  use  for  sulfuring. 


Fungicides 


459 


No  matter  what  type  of  machine  is  in  use,  it  is  essential 
to  keep  on  hand  a  supply  of  any  parts  that  may  be  broken  or 


235.  —  Sulfuring  machine  in  use.    After  Faurot.- 


become  worn  out.  The  best  companies  are  prompt  in  filh'ng 
orders  for  repairs,  but  the  grower  cannot  afford  loss  of  even  a 
very  short  time  at  critical  periods. 


SOIL   DISINFFXTION  "^''^ 

Soil  disinfection  in  the  field  has  as  yet  in  the  main  proved 
impracticable.  All  promising  chemicals  have  been  tried 
without  avail.  Electricity  has  not  given  beneficial  results, 
and  at  present  there  is  no  hope  of  any  practicable  manner  of 
ridding  fields  of  parasites  by  any  process  of  disinfection.  In 
a  few  instances  large  applications  of  lime,  formalin,  or  sulfur 
have  proved  beneficial  (see  sweet  potato,  onion,  etc.),  but 
the  general  practicability  of  such  usage  is  doubtful. 

Disinfection  of  limited  areas  is,  however,  practicable,  is 
largely  employed,  and  has  already  resulted  in  great  benefit, 
eliminating  not  only  injurious  fungi  but  insects  and  weeds  as 
well.  Cutting  benches,  flats,  and  other  benches  in  the  green- 
house, cold  frames,  and  seed  beds,  and  other  small  areas 
may  be  disinfected  with  advantage.  The  means  to  be  em- 
ployed depend  upon  the  area,  its  location,  and  the  facilities  at 
hand.    The  leading  methods  are  given  below: 

Baking.  —  Flats,  pots,  and  other  small  containers  of 
earth  may  often  be  satisfactorily  disinfected  by  placing 
them  upon  a  boiler  or  over  a  stove,  or  in  an  oven  for  a  com- 
paratively long  period. 

Permanent  steam  disinfectors.  —  A  system  of  13^-inch 
pipes,  which  are  p<Mforat(Hl  with  j 4-inch  holes  on  their  under 
side  at  intervals  of  6  inches  throughout  their  entire  length, 
may  be  placed  about  one  foot  below  the  surface  of  the  soil. 
The  pipes  should  run  lengthwise  of  the  bed,  18  inches  apart, 
and  be  connected  with  a  steam  boiler.  Before  treatment  the 
soil  should  be  thoroughly  spaded  up  and  pulverized  to  permit 
ready  access  of  the  steam  to  all  parts,  and  all  fertilizers  except 
commercial  ones  should  be  applied  at  this  time,  since  fresh 
spores  of  the  fungus  are  likely  to  be  carried  in  if  manure  be 
added  after  disinfection. 

460 


Soil  Disinfection  461 

The  seed  bed  should  be  covered  with  several  thicknesses  of 
old  burlap  or  blankets  to  confine  the  heat  to  the  soil.  The 
steam  should  be  applied  at  a  pressure  of  from  80  to  150 
pounds,  since  at  high  pressure  the  soil  does  not  become  so 
wet  as  when  low-pressure  steam  is  used.  A  treatment  of  from 
one  to  two  hours  is  usually  sufficient  to  disinfect  thoroughly 
the  soil  to  a  depth  of  18  inches.  A  few  potatoes  laid  in  the 
surfaces  oil  will  indicate  the  thoroughness  of  the  treatment 
by  the  degree  to  which  they  are  cooked.  The  blankets  may 
advantageously  be  left  on  for  some  time. 

While  this  method  offers  some  advantages  for  seed  beds 
of  limited  area,  in  that  the  pipes  may  be  left  in  the  ground 
and  used  year  after  year  with  little  extra  labor  and  may 
also  be  used  for  subirrigation,  the  initial  cost  of  installa- 
tion, especially  on  large  seed-bed  areas,  may  be  prohibitive. 

Inverted-pan  method.  —  The  method  which  has  given 
the  best  results  in  practice,  and  which  because  of  its  simplic- 
ity and  small  cost  recommends  itself  for  use  on  large  or 
small  areas,  is  the  invention  of  Mr.  A.  D.  Shamel,  of  the 
U.  S.  Dept.  Agr.  Bur.  of  Plant  Industry,  and  was  devised 
by  him  to  disinfect  nematode-infested  soils  in  Florida.  The 
apparatus  consists  of  a  galvanized  iron  pan,  6'  x  10'  x  6" 
which  is  inverted  over  the  soil  and  the  steam  admitted  under 
pressure.  The  pan  is  supplied  with  steam-hose  connections, 
has  sharp  edges,  which  are  forced  into  the  soil  on  all  sides  to 
prevent  the  escape  of  steam,  and  is  fitted  with  handles  for 
moving  it  from  place  to  place,  the  weight  of  the  entire  pan 
bemg  not  over  400  pounds. 

The  soil  is  prepared  as  in  the  greenhouse  method,  a  few 
potatoes  being  buried  at  a  depth  of  a  foot  to  gauge  the 
degree  of  heat  attained,  or  a  soil  thermometer  may  be  used  if 
desired.  The  steam  should  be  kept  at  as  high  pressure  as 
possible,  from  80  to  150  pounds  being  best,  and  the  treatment 
should  continue  from  30  to  60  minutes,  depending  upon  the 
pressure  maintained  and  the  character  of  the  soil.  Wet  soils 
require  more  time  than  dry  soils.  In  experiments  conducted 
on  tobacco  seed  beds  in  the  spring  of  1907,  one  hour's  steam- 


462 


Diseases  of  Economic  Plants 


ing  at  80°  C.  gave  best  results  in  killing  both  the  fungi  and 
the  weed  seeds.  When  one  section  of  the  bed  is  treated,  the 
pan  is  lifted  and  carried  to  another  portion,  and  the  operation 
repeated  until  the  entire  bed  is  steamed. 


Fig.  236.  —  Disinfecting  with  steam  by  the  inverted-pan  method. 
After  Johnson. 


The  inverted-pan  method  is  particularly  applicable  in 
disinfecting  greenhouse  benches  or  flats.  Streaming  steam 
from  the  heating  system  passed  into  the  pan  for  one  and  one- 
half  hours  suffices.  A  steam  hose  connecting  the  pan  with  a 
traction  engine  makes  a  serviceable  out-of-door  outfit. 

The  Sargent  method.  —  Disinfection  by  a  system  of 
steam  pipes  arranged  in  the  form  of  a  harrow,  with  hollow, 


Soil  Disinfection 


463 


perforated  teeth,  has  proved  satisfactory  under  some  condi- 
tions. 

Surface  firing.  —  Surface  firing  of  seed  beds  has  been  a 
common  practice  for  years  in  some  tobacco  sections,  par- 
ticularly in  Kentucky  and  other  southern  states,  the  end  in 
view  being  the  improvement  of  the  tilth  of  the  soil  and  the 
killing  of  weed  seeds  rather  than  the  destruction  of  any 
fungous  disease.    In  Italy  burning  is  now  considered  a  part 


Fig.  237.  —  Disinfecting  soil  with  a  Sargent  disinfector.    Original. 

of  the  regular  method  of  tobacco  seed-bed  preparation,  it 
having  been  resorted  to  as  a  preventive  of  root-rot  due  to 
Thielavia. 

Two  methods  of  surface  firing  are  in  vogue;  the  first, 
by  direct  firing,  the  second  requiring  the  use  of  a  pan.  In 
the  direct  method,  the  land  to  be  disinfected  is  first  thor- 
oughly pulverized  and  manure  applied.  It  is  then  covered 
with  straw,  brush,  and  wood  sufficient  to  make  a  hot  fire. 
This  is  ignited  and  allowed  to  burn  an  hour  or  so,  after 
which  the  ashes  are  raked  into  the  surface  soil. 

The  second  method,  pan  firing,  consists  in  the  use  of  a 
sheet-iron  pan,  3'  by  9',  which  is  set  in  the  middle  of  the  seed 


464  Diseases  of  Economic  Plants 

bed  and  a  fire  built  under  it.  The  soil  on  one  side  of  the  pan 
to  a  depth  of  6  inches  is  shoveled  and  heated,  great  care  being 
taken  to  keep  it  moist,  otherwise  the  humus  would  be  burned 
out  and  the  physical  texture  seriously  altered.  After  an 
hour  this  soil  is  put  back  and  that  from  the  other  side  of  the 
pan  subjected  to  the  same  treatment,  and  then  the  pan 
moved  along  to  a  new  place.  The  soil  underneath  the  pan 
itself  is  thereby  subjected  to  heat  for  two  hours. 

Disinfection  by  formalin.  —  The  use  of  formalin  for  the 
disinfection  of  greenhouse  soil  and  of  tobacco  seed  beds 
against  Corticium  has  been  in  vogue  for  some  time  with 
excellent  results.  It  furnishes  a  very  simple  means  of  disin- 
fection as  follows:  The  beds  are  thoroughly  prepared  as  for 
the  other  methods  of  disinfection  described  and  are  then 
drenched  with  a  2  per  cent  formalin  solution  using  two 
quarts  of  this  solution  to  the  square  foot  of  bed  space.  The 
solution  should  be  put  on  with  a  watering  pot  with  a  rose 
orifice  and  distributed  as  evenly  as  possible  over  the  bed,  so 
as  to  wet  the  soil  thoroughly  to  the  depth  of  a  foot.  It  will, 
in  most  cases,  be  necessary  to  put  this  solution  on  in  two  or 
three  applications,  as  the  soil  will  not  immediately  take 
in  this  quantity  of  water.  The  beds  should  then  be  covered 
with  heavy  burlap  or  a  tarpaulin  to  retain  the  fumes  for  a  day 
or  so,  and  then  aired  for  a  week  before  sowing  the  seed. 

Spring  applications  of  formalin  are  open  to  the  following 
objections:  The  addition  of  such  a  large  quantity  of  water 
to  the  soil  keeps  it  wet  and  cold  longer  than  would  naturally 
be  the  case,  thus  delaying  germination  as  well  as  subsequent 
growth;  the  necessity  of  airing  the  beds  to  remove  the  for- 
malin fumes  and  to  allow  the  soil  to  dry  out  also  causes  delay 
in  seeding.  To  obviate  these  difficulties  the  beds  should  be 
treated  in  the  fall,  before  freezing. 

Disinfection  by  sulfuric  acid.  —  One-eighth  to  three- 
sixteenths  fluid  ounce  of  commercial  sulfuric  acid  in  from  one 
to  two  pints  of  water,  according  to  the  humidity  of  the  soil,  is 
applied  per  square  foot  of  soil  immediately  after  the  seeds  are 
covered.     This  treatment  is  used  principally  for  conifers. 


Soil  Disinfection  465 

Abundant  watering  is  necessary  to  prevent  root  injury  of  the 
seedlings. 

Disinfection  by  copper-sulfate.  —  This  chemical  may  be 
used  up  to  one-fourth  ounce  per  square  foot.  It  is  employed 
chiefly  for  conifer  seed  beds. 

Disinfection  by  zinc-chlorid.  —  Five-eighths  of  an  ounce 
of  this  solution  per  square  foot  may  be  employed  for  conifer 
seed  beds,  but  it  is  more  expensive  than  copper-sulfate. 

Disinfection  by  hot  water.  ^^^  Pots,  flats,  etc.,  may  be 
disinfected  by  submersion  in  hot  water,  98°  C.  (208°  F.)  for 
five  minutes.  The  quantity  of  water  necessary  increases 
with  the  volume  of  soil  to  be  treated ;  thus  for  8"  pots  about 
3000  cc.  of  water  is  needed  at  98°  C.  or  2000  cc.  of  boiling 
water.  On  shallow  benches  boiling  water  should  be  used  at 
the  rate  of  7  gallons  per  cubic  foot  of  soil. 


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BIBLIOGRAPHY 

1.  Whetzel,  H.  H.,  An  outline  of  the  history  of  phytopathology. 
W.  B.  Saunders  Co.  1918.  2.  Sorauer,  P.,  Manual  of  plant  diseases. 
Trans,  by  F.  Dorrance,  Dorranceville,  Pa.  1914.  3.  Lodeman,  E. 
G.,  The  spraying  of  plants,  6.  The  Macmillan  Co.  1913.  4. 
Stevens,  F.  L.,  Some  problems  in  plant  pathology  in  reference  to 
transportation.  Phytop.  5:  108.  1915.  5.  Coons,  G.  H.,  and  Nel- 
son, R.,  The  plant  diseases  of  importance  in  the  transportation  of 
fruit  and  vegetables.  Am.  R.  R.  Per.  Fr.  Assn.  Cir.  ^73.  1918.  6. 
Lyman,  G.  R.,  War  Emergency  Board,  American  Plant  Pathologists, 
Midyear  Rept.  June  25,  1918.  7.  Roberts,  J.  W.,  and  Pierce  L., 
Control  of  cherry  leaf -spot.  U.  S.  Dept.  Agr.  Farms'.  Bui.  1053. 
1919.  8.  Beinhardt,  E.  G.,  Steam  sterilization  of  seed  beds  for 
tobacco  and  other  crops.  U.  S.  Dept.  Agr.  Farais'.  Bui.  996. 
1918.  9.  Selby,  A.  D.,  and  Humbert,  J.  A.,  Methods  of  soil  steriliza- 
tion for  plant  beds  and  greenhouses.  Ohio  Agr.  Exp.  Sta.  Cir. 
151.  1915.  10.  Johnson,  J.,  The  control  of  damping-off  disease 
in  plant  beds.  Wis.  Agr.  Exp.  Sta.  Res.  Bui.  5^  1914.  11.  Hart- 
ley, C,  and  Pierce,  R.  G.,  The  control  of  damping-off  of  coniferous 
seedlings.  U.  S.  Dept.  Agr.  Bui.  Jf53.  1917.  12.  Gifford,  C.  M., 
The  dampirg-off  of  coniferous  seedlings.  Vt.  Agr.  Exp.  Sta.  Bui. 
157.  1911.  13.  Peltier,  G.  L.,  Parasitic  Rhizoctonias  in  Amer- 
ica. 111.  Agr.  Exp.  Sta.  Bui.  189.  1916.  14.  Pammel,  L.  H., 
Fungous  diseases  of  sugar  beets.  la.  Agr.  Exp.  Sta.  Bui.  15.  1891. 
16.  Fulton,  H.  R.,  Diseases  of  pepper  and  beans.  La.  Agr.  Exp. 
Sta.  Bui.  101.  1908.  16.  Pammel,  L.  H.,  Cotton  root-rot.  Tex. 
Agr.  Exp.  Sta.  Rept.  2:  61.  1898.  17.  Duggar,  B.  M.,  The  Texas 
root-rot  fungus  and  its  conidial  stage.  Ann.  Mo.  Bot.  Gard.  3.  1916. 
18.  Gilbert,  W.  W.,  The  root-rot  of  tobacco  caused  by  Thielavia 
basicola.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  158.  1909.  19.  John- 
son, J.,  Host  plants  of  Thielavia  basicola.  Jour.  Agr.  Res.  7: 
289.  1916.  20.  Stevens,  F.  L.,  and  Sackett,  W.  G.,  The  Gran- 
ville tobacco  wilt.  N.  C.  Agr.  Exp.  Sta.  Bui.  188.  1903.  21. 
Stone,  G.  E.,  and  Smith,  R.  E.,  Nematode  worms.  Mass.  Agr. 
467 


468  Bibliography 

Exp.  Sta.  Bui.  55.  1898.  22.  Bessey,  E.  E.,  and  Byars,  L.  P., 
The  control  of  root-knot.  U.  S.  Dept.  Agr.  Farms'.  Bui.  648.  1915. 
23.  Bessey,  E.  E.,  Root-knot  and  its  control.  U.  S.  Dept.  Agr., 
B.  P.  I.  Bui.  ^i7.  1911.  24.  Widtsoe,  J.  A.,  The  relation  of  smelter 
smoke  to  Utah  agriculture.  Utah  Agr.  Exp.  Sta.  Bui.  8S.  1903. 
25.  Bakke,  A.  L.,  The  effect  of  city  smoke  on  vegetation.  la.  Agr. 
Exp.  Sta.  Bui.  145.  1913.  26.  Arthur,  J.  C,  History  and  scope 
of  plant  pathology.  Cong.  Arts  and  Sc.  5:  149.  1906.  27.  Waite, 
M.  B.,  Vegetable  pathology  an  economic  science.  Cong.  Arts 
and  Sc.  5;  165.  1906.  28.  Hesler,  L.  R.,  and  Whetzel,  H.  H., 
Manual  of  fruit  diseases.  The  Macmillan  Co.  1917.  29.  Schrenk, 
H.  V,  and  Spaulding,  P.,  The  bitter-rot  of  apples.  U.  S.  Dept. 
Agr.,  B.  P.  I.  Bui.  4-^.  1903.  30.  Burrill,  T.  J.,  Bitter-rot  of  apples. 
111.  Agr.  Exp.  Sta.  Bui.  118.  1907.  31.  Blair,  J.  C,  Bitter-rot  of 
apples.  111.  Agr.  Exp.  Sta.  Bui.  117.  1907.  32.  Roberts,  J.  W., 
and  Pierce,  L.,  Apple  bitter-rot  and  its  control.  U.  S.  Dept.  Agr. 
Farms'.  Bui.  938.  1918.  33.  Roberts,  J.  W.,  The  sources  of  apple 
bitter-rot  infections.  U.  S.  Dept.  Agr.  Bui.  684.  1918.  34.  Wal- 
lace, E.,  The  scab  disease  of  apples.  N.  Y.  (Cornell)  Agr.  Exp.  Sta. 
Bui.  335.  1913.  35.  Morris,  H.  E.,  A  contribution  to  our  knowl- 
edge of  apple  scab.  Mont.  Agr.  Exp.  Sta.  Bui.  96.  1914.  36. 
Scott,  W.  M.,  and  Rorer,  J.  B.,  Apple  blotch.  U.  S.  Dept.  Agr., 
B.  P.  I.  Bui.  144.  1909.  37.  Lewis,  D.  E.,  The  control  of  apple 
blotch.  Kan.  Agr.  Exp.  Sta.  Bui.  19U.  1913.  38.  Clinton,  G.  P., 
Apple-rot  in  Illinois.  111.  Agr.  Exp.  Sta.  Bui.  69.  1902.  39.  Scott, 
W.  M.,  and  Quaintance,  A.  L.,  Spraying  for  apple  diseases  and  the 
codling  moth  in  the  Ozarks.  U.  S.  Dept.  Agr.  Fanns'.  Bui.  283. 
1907.  40.  Roberts,  J.  W.,  Apple  blotch  and  its  control.  U.  S. 
Dept.  Agr.  Bui.  534.  1917.  41.  Reed,  H.  S.,  and  Crabill,  C.  H., 
The  cedar  rust  disease  of  apples  caused  by  Gymnosporangium 
juniperi-virginianse  Schw.  Va.  Agr.  Exp.  Sta.  Tech.  Bui.  9.  1915. 
42.  Jones,  L.  R.,  and  Bartholomew,  E.  T.,  Apple  rust  and  its  con- 
trol in  Wisconsin.  Wis.  Agr.  Exp.  Sta.  Bui.  257.  1915.  43.  Whet- 
zel, H.  H.,  The  blight  canker  of  apple  trees.  N.  Y.  (Cornell)  Agr. 
Exp.  Sta.  Bui.  236.  1906.  44.  Hesler,  L.  R.,  Black-rot,  leaf-spot, 
and  canker  of  pomaceous  fruits.  N.  Y.  (Cornell)  Agr.  Exp.  Sta. 
Bui.  379.     1916.     45.  Paddock,  W.,  The  New  York  apple  tree 


Bibliography  469 

canker.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  163.  1899.  46. 
Stevens,  F.  L.,  and  Hall,  J.  G.,  Some  apple  diseases.  N.  C.  Agr. 
Exp.  Sta.  Bui.  196.  1907.  47.  Lawrence,  W.  H.,  Black  spot 
canker.  Wash.  Agr.  Exp.  Sta.  Bui.  66.  1904.  48.  Cordley,  A.  B., 
Apple  tree  anthracnose.  Ore.  Agr.  Exp.  Sta.  Bui.  60.  1900. 
49.  Hasselbring,  H.,  Canker  of  apple  trees.  111.  Agr.  Exp.  Sta. 
Bui.  70.  1902.  50.  Gloyer,  W.  O.,  Apple  blister  canker  and  meth- 
ods of  treatment.  Ohio  Agr.  Exp.  Sta.  Cir.  125.  1912.  51.  Cooper, 
J.  R.,  Studies  of  the  etiology  and  control  of  blister  canker  on  apple 
trees.  Neb.  Agr.  Exp.  Sta.  Res.  Bui.  1£.  1917.  52.  Paddock, 
W.,  European  apple  tree  canker  in  America.  Sc.  n.  s.  12:  297. 
1900.  53.  Crabill,  C.  H.,  The  frog-eye  leaf  spot  of  apples.  Va. 
Poly.  Inst.  Bui.  209.  1915.  54.  Lewis,  I.  M.,  Apple  leaf-spot. 
N.  H.  Agr.  Exp.  Sta.  Rept.  19-20:  365.  1908.  55.  Sheldon,  J.  L., 
Another  leaf-spot  fungus  of  the  apple.  Torreya  S:  139.  1908. 
56.  Stevens,  F.  L.,  and  Hall,  J.  G.,  Hypochnose  of  pomaceous 
fruits.  Ann.  Myc.  7:  49.  1909.  57.  Burt,  E.  A.,  Corticiums 
causing  Pellicularia  disease  of  the  coffee  plant,  hypochnose  of 
pomaceous  fruits  and  Rhizoctonia  disease.  Ann.  Mo.  Bot.  Gard. 
5:  119.  1918.  58.  Eustace,  H.  J.,  A  destructive  apple  rot  following 
scab.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  227.  1902.  59.  Eustace, 
H.  J.,  Two  decays  of  stored  apples.  N.  Y.  (Geneva)  Agr.  Exp.  Sta. 
Bui.  235.  1903.  60.  Clinton,  G.  P.,  Apple  rots  of  Illinois.  111. 
Agr.  Exp.  Sta.  Bui.  69.  1902.  61.  Ballard,  W.  S.,  Apple  powdery 
mildew  and  its  control  in  the  Pajaro  Valley.  IT.  S.  Dept.  Agr. 
Bui.  120.  1914.  62.  Fisher,  D.  F.,  Apple  powdery  mildew  and  its 
control  in  the  arid  regions  of  the  Pacific  Northwest.  U.  S.  Dept. 
Agr.  Bui.  712.  1918.  63.  Stevens,  F.  L.,  and  Hall,  J.  G.,  Some 
apple  diseases.  The  Volutella  rot.  N.  C.  Agr.  Exp.  Sta.  Bui.  196. 
1907.  64.  Brooks,  Charles,  The  fruit  spot  of  apples.  N.  H.  Agr. 
Exp.  Sta.  Rept.  19-20.  1908.  65.  Wilcox,  E.  M.,  A  rhizomorphic 
root  rot  of  fruit  trees.  Okla.  Agr.  Exp.  Sta.  Bui.  49.  1901.  66. 
Wolf,  F.  A.,  and  Cromwell,  R.  O.,  Xylaria  root  rot  of  apple.  Jour. 
Agr.  Res.  9:  269.  1917.  67.  Home,  W.  T.,  Wood  decay  in  orchard 
trees.  Cal.  Agr.  Exp.  Sta.  Cir.  137.  1915.  68.  McAlpine,  Bitter 
pit  investigation.  Repts.  1,  2,  3,  4.  Australia.  1911-1915.  69. 
Scott,  W.  M.,  and  Roberts,  J.  W.,  The  Jonathan  fruit-spot.    U.  S. 


470  Bibliography 

Dept.  Agr.,  B.  P.  I.  Cir.  11£.  1913.  70.  Morse,  W.  J.,  and  Lewis, 
C.  E.,  Maine  apple  diseases.  Me.  Agr.  Exp.  Sta.  Bui.  185.  1910. 
71.  Brooks,  Chas.,  Some  apple  diseases  and  their  treatment.  N.  H. 
Agr.  Exp.  Sta.  Bui.  157.  1902.  72.  Roberts,  J.  W.,  The  rough 
bark  disease  of  the  Yellow  Newton  apple.  U.  S.  Dept.  Agr.,  B.  P. 
I.  Bui.  280:  7.  1913.  73.  Burrill,  T.  J.,  Trans.  111.  Hort.  Soc.  for 
1878,  12:  80.  1879.  74.  Waite,  M.  B.,  The  cause  and  prevention 
ofpearbhght.  U.  S.  Dept.  Agr.  Yearbook.  295.  1895.  75.  Whet- 
zel,  H.  H.,  and  Stewart,  V.  B.,  Fire  blight  of  pears,  apples,  quinces, 
etc.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  272.  1909.  76.  Stevens, 
F.  L.,  Ruth,  W.  A.,  and  Spooner,  C.  S.,  Pear  blight  wind  borne. 
Sc.  48:  449.  1918.  77.  Smith,  R.  E.,  Pear  scab.  Cal.  Agr.  Exp. 
Sta.  Bui.  i05.  1905.  78.  Swingle,  D.  B.,  Fruit  diseases  in  Montana. 
Mont.  Agr.  Exp.  Sta.  Cir.  37.  1914.  79.  Duggar,  B.  M.,  Some 
important  pear  diseases.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui. 
145.  1898.  80.  Halsted,  B.  D.,  Some  fungous  diseases  of  the 
quince.  N.  J.  Agr.  Exp.  Sta.  Bui.  91.  1892.  81.  Smith,  R.  E., 
California  plant  diseases.  Cal.  Agr.  Exp.  Sta.  Bui.  218.  1911. 
82.  Paddock,  W.,  An  apricot  blight.  Colo.  Agr.  Exp.  Sta.  Bui.  84. 
1903.  83.  Higgins,  B.  B.,  Contribution  to  the  life  history  and 
physiology  of  Cylindrosporium  on  stone  fruits.  Am.  Jour.  Bot. 
1:  145.  1914.  84.  Keitt,  G.  W.,  Control  of  cherry  leaf  spot  in 
Wisconsin.  Wis.  Agr.  Exp.  Sta.  Bui.  ^Sg.  1918.  85.  Scott,  W.  M., 
Lime-sulfur  mixtures  for  the  summer  spraying  of  orchards.  IT.  S. 
Dept.  Agr.,  B.  P.  L  Cir.  27.  1909.  86.  Jackson,  H.  S.,  Diseases  of 
drupaceous  fruits.  Ore.  Crop  Pest  and  Hort.  Bien.  Rept.  1911-  . 
1912:  250.  1913.  87.  Stewart,  V.  B.,  Some  important  leaf  diseases 
of  nursery  stock.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  358.  1915. 
88.  Heald,  F.  D.,  Tree  fruits.  Neb.  Agr.  Exp.  Sta.  Rept.  19:  29. 
1906.  89.  Scott,  W.  M.,  and  Quaintance,  A.  L.,  Spraying  peaches 
for  the  control  of  brown  rot,  scab,  and  curculio.  IT.  S.  Dept.  Agr. 
Farms'.  Bui.  44O.  1911.  90.  Smith,  E.  F.,  Peach  blight.  Jour. 
Myc.  7.-36.  1891.  91.  Wormald,  H.,  The  Cytospora  disease  of  the 
cherry.  Jour.  So.  E.  Agr.  Coll.  Wye  (England)  1912:  367.  1914. 
92.  Keitt,  G.  W.,  Peach  scab  and  its  control.  U.  S.  Dept.  Agr. 
Bui.  395.  1917.  93.  Pierce,  N.  B.,  Peach  leaf  curl,  its  nature  and 
treatment.   U.  S.  Dept.  Agr.  Div.  Veg.  Phys.  &  Path.  Bui.  20.    1900. 


Bibliography  471 

94.  Rolfs,  F.  M.,  Winter  killing  of  twigs,  cankers,  and  sun  scald 
of  peach  trees.  Mo.  St.  Fruit  Farm  Bui.  17.  1910.  95.  Smith, 
R.  E.,  California  peach  blight.  Cal.  Agr.  Exp.  Sta.  Bui.  i5i.  1907. 
96.  Hedgcock,  G.  G.,  The  cross  inoculation  of  fruit  trees  and  shrubs 
with  crown  gall.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  131.  1908.  97. 
Smith,  E.  F.,  and  Townsend,  C.  O.,  A  plant  tumor  of  bacterial 
origin.  Sc.  n.  s.  23:  671.  1907.  98.  Townsend,  C.  0.,  A  bacterial 
gall  of  the  daisy  and  its  relation  to  gall  formation  on  other  plants. 
Sc.  n.  s.  29:  273.  1909.  99.  Swingle,  D.  B.,  and  Morris,  H.  E., 
Crown-gall  injury  in  the  orchard.  Mont.  Agr.  Exp.  Sta.  Bui.  121. 
1918.  100.  Smith,  E.  F.,  Brown,  N.  A.,  and  Townsend,  C.  O., 
Crown  gall  of  plants.    IT.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  213.    1911. 

101.  Smith,  E.  F.,  et  al.,  The  structure  and  development  of  crown 
gall:  a  plant  cancer.    U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  255.     1912. 

102.  Hedgcock,  G.  G.,  Field  studies  of  the  crown-gall  and  hairy- 
root  of  the  apple  tree.    U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  186.    1910. 

103.  Rolfs,  F.  M.,  A  bacterial  disease  of  stone  fruits.  N.  Y.  (Cor- 
nell) Agr.  Exp.  Sta.  Mem.  8.  1915.  104.  Roberts,  J.  W.,  Control 
of  peach  bacterial  spot  in  southern  orchards.  U.  S.  Dept.  Agr. 
Bui.  543.  1917.  105.  Smith,  E.  F.,  Observations  on  a  hitherto  un- 
reported bacterial  disease  the  cause  of  which  enters  the  plant  through 
ordinary  stomata.  Sc.  n.  s.  17:  456.  1903.  And  Bacteria  in  rela- 
tion to  plant  disease,  I,  Figs.  11,  15,  70,  71,  72,  and  PL  19.  106. 
Rorer,  J.  B.,  A  bacterial  disease  of  the  peach.  Mycologia  1:  23. 
1909.  107.  Selby,  A.  D.,  Preliminary  report  upon  diseases  of  the 
peach.  Ohio  Agr.  Exp.  Sta.  Bui.  92.  1898.  108.  Atkinson,  G.  F., 
A  new  anthracnose  of  the  privet.  N.  Y.  (Cornell)  Agr.  Exp.  Sta. 
Bu\.49.  1892.  109.  Smith,  E.  F.,  Peach  yellows  and  peach  rosette. 
U.  S.  Dept.  Agr.  Farms'.  Bui.  17:  7.  1894.  110.  Smith,  E.  F., 
Additional  evidence  on  the  communicability  of  peach  yellows  and 
peach  rosette.  U.  S.  Dept.  Agr.  Div.  Veg.  Path.  Bui.  1.  1891. 
111.  Smith,  E.  F.,  Notes  on  the  Michigan  disease  known  as  "Little 
Peach."  Fenville  (Mich.)  Herald,  October  15,  1898.  112.  Blake, 
M.  A.,  Peach  yellows  and  little  peach.  N.  J.  Agr.  Exp.  Sta.  Bui. 
226:  10.  1910.  113.  Farlow,  W.  G.,  The  black  knot.  Bussey 
Inst.  Bui.  1876:  440.  1876.  114.  Galloway,  B.  F.,  Plum  pockets. 
U.  S.  Agr.  Commr.  Rept.  1888:  366.    1889.    115.  Whetzel,  H.  H., 


472  Bibliography 

and  Stewart,  V.  B.,  Fire  blight  of  pears,  apples,  quinces,  etc.  N.  Y. 
(Cornell)  Agr.  Exp.  Sta.  Bui.  272.  1909.  116.  Jones,  L.  R.,  Studies 
upon  plum  blight.  Centrbl.  f.  Parasitenk.  u.  Infek.  2  (Abt.  II), 
825.  117.  Higgins,  B.  B.,  Plum  wilt.  Ga.  Agr.  Exp.  Sta.  Bui.  HS. 
1916.  118.  Burkholder,  W.  H.,  The  anthracnose  disease  of  the 
raspberry  and  related  plants.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui. 
395.  1917.  119.  Rees,  H.  L.,  Experimental  spraying  for  black- 
berry anthracnose.  Wash.  Agr.  Exp.  Sta.  Mo.  Bui.  3.  1915.  120. 
Lawrence,  W.  H.,  Anthracnose  of  the  blackberry  and  raspberry. 
Wash.  Agr.  Exp.  Sta.  Bui.  97.  1910.  121.  CUnton,  G.  P.,  Orange 
rust  of  raspberry  and  blackberry.  111.  Agr.  Exp.  Sta.  Bui.  29.  1893. 
122.  Stone,  G.  E.,  and  Smith,  R.  E.,  A  late  rust  of  the  blackberry. 
Mass.  (Hatch)  Agr.  Exp.  Sta.  Rept.  9:  74.  1897.  123.  Lawrence, 
W.  H.,  Bluestem  of  the  black  raspberry.  Wash.  Agr.  Exp.  Sta. 
Bui.  108.  1912.  124.  Shear,  C.  L.,  Cranberry  diseases.  U.  S. 
Dept.  Agr.,  B.  P.  I.  Bui.  110.  1907.  125.  Halsted,  B.  D.,  Some 
fungous  diseases  of  the  cranberry.  N.  J.  Agr.  Exp.  Sta.  Bui.  64. 
1889.  126.  Franklin,  H.  J.,  Report  of  the  cranbeny  substation  for 
1916.  Mass.  Agr.  Exp.  Sta.  Bui.  180.  1917.  127.  Shear,  C.  L., 
End  rot  of  cranberries.  Jour.  Agr.  Res.  11:  35.  1917.  128.  Du- 
rand,  E.  J.,  A  disease  of  currant  canes.  N.  Y.  (Cornell)  Agr.  Exp. 
Sta.  Bui.  125.  1897.  129.  Grossenbacher,  J.  G.,  and  Duggar, 
B.  M.,  A  contribution  to  the  life  history,  parasitism,  and  biology  of 
Botryosphaeria  ribis.  N.  Y.  (Geneva)  Agr.  E.xp.  Sta.  Tech.  Bui. 
18.  1911.  130.  Pammel,  L.  H.,  Spot  diseases  of  currants  and 
gooseberries.  la.  Agr.  Exp.  Sta.  Bui.  13.  1891.  131.  Stewart, 
V.  B.,  Some  important  leaf  diseases  of  nursery  stock.  N.  Y.  (Cor- 
nell) Agr.  Exp.  Sta.  Cir.  32.  1916.  132.  Stewart,  F.  C,  and  Eus- 
tace, H.  J.,  An  epidemic  of  currant  anthracnose.  N.  Y.  (Geneva) 
Agr.  Exp.  Sta.  Bui.  199.  1901.  133.  Cook,  M.  T.,  The  double 
blossom  of  the  dewberry.  Del.  Agr.  Exp.  Sta.  Bui.  93.  1911. 
134.  Close,  C.  P.,  Treatment  for  gooseberry  mildew.  N.  Y,  (Gen- 
eva) Agr.  Exp.  Sta.  Bui.  161.  1899.  135.  Giddings,  N.  J.,  Infec- 
tion and  immunity  in  apple  rust.  W.  Va.  Agr.  Exp.  Sta.  Bui,  170. 
1918.  136.  Shear,  C.  L.,  Miles,  G.  F.,  and  Hawkins,  L.  A.,  The 
control  of  black-rot  of  the  grape.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui. 
155.    1909.     137.  Wilson,  C.  S.,  and  Reddick,  D.,  The  black  rot  of 


Bibliography  473 

the  grape  and  its  control.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui. 
266.  1909.  138.  Reddick,  D.,  The  black  rot  disease  of  grapes. 
N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  293.  1911.  139.  Edson,  A.  W., 
The  black  rot  of  grapes  in  North  Carolina  and  its  treatment.  N.  C. 
Agr.  Exp.  Sta.  Bui.  185.  1903.  140.  Bioletti,  F.  T.,  Oidium  or 
powdery  mildew  of  the  vine.  Cal.  Agr.  Exp.  Sta.  Bui.  186.  1907. 
141.  Farlow,  W.  G.,  On  the  American  grape-vine  mildew.  Bussey 
Inst.  Bui.  1.  1876.  142.  Quaintance,  A.  L.,  and  Shear,  C.  L.,  In- 
sect and  fungous  enemies  of  the  grape  east  of  the  Rocky  Mountains. 
U.  S.  Dept.  Agr.  Farms'.  Bui.  284.  1907.  143.  Hawkins,  L.  A., 
Experiments  in  the  control  of  grape  anthracnose.  U.  S.  Dept.  Agr., 
B.  P.  I.  Cir.  105.  1913.  144.  Reddick,  D.,  Dead  arm  disease  of 
grapes.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  389.  1914.  145.  Red- 
dick, D.,  Necrosis  of  the  grape  vine.  N.  Y.  (Cornell)  Agr.  Exp.  Sta. 
Bui.  263.  1909.  146.  Pierce,  N.  B.,  The  California  vine  disease. 
U.  S.  Dept.  Agr.,  Div.  Veg.  Phys.  and  Path.  Bui.  2.  1892.  147. 
Hedgcock,  G.  G.,  Field  studies  of  the  crown-gall  of  the  grape. 
U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  iS3.  1910.  148.  Stubenrauch,  A.  V., 
Factors  governing  the  successful  storage  of  California  table  grapes. 
U.  S.  Dept.  Agr.  Bui.  35.  1913.  149.  Gladwin,  F.  E.,  A  non- 
parasitic malady  of  the  vine.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui. 
J^Jf.9.  1918.  150.  Paddock,  W.,  Anthracnose  of  the  black  rasp- 
berry. N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  124.  1897.  151. 
Stewart,  F.  C,  and  Eustace,  H.  J.,  Raspberry  cane  blight  and 
raspberry  yellows.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  226.  1902. 
152.  Sackett,  W.  G.,  Spur  blight  of  the  red  raspberry  caused  by 
Sphffirella  rubina.  Colo.  Agr.  Exp.  Sta.  Bui.  206.  1915.  153. 
Garman,  H.,  Some  strawberry  pests.  Ky.  Agr.  Exp.  Sta.  Bui.  31. 
1890.  154.  Hume,  H.  H.,  Strawberry  leaf  spot.  Fla.  Agr.  Exp. 
Sta.  Rept.  95.  1901.  155.  Stevens,  F.  L.,  A  destructive  strawberry 
disease.  Sc.  n.  s.  ^fi*.- 949.  1914.  156.  Halsted,  B.  D.,  A  new  straw- 
berry leaf  blight.  N.  J.  Agr.  Exp.  Sta.  Rept.  329.  1893.  157. 
Stevens,  F.  L.j  and  Peterson,  A.,  Some  new  strawberry  fungi. 
Phytop.  6:  259.  1916.  158.  Cook,  Mel.  T.,  Diseases  of  tropical 
plants.  Macmillan  &  Co.  1913.  159.  Smith,  R.  E.,  The  brown- 
rot  of  the  lemon.  Cal.  Agr.  Exp.  Sta.  Bui.  190.  1907.  160.  Stev- 
ens, H.  E.,  Florida  citrus  diseases.    Fla.  Agr.  Exp.  Sta.  Bui.  150. 


474  Bibliography 

1918.  161.  Rorer,  J.  B.,  Enfermedades  y  plagas  del  cacao  en  el 
Ecuador  y  metodos  modernos  apropiados  al  cultivo  del  cacao.  1918. 
162.  Smith,  C.  0.,  Cottony  rot  of  lemons  in  California.  Cal.  Agr. 
Exp.  Sta.  Bui.  265.  1916.  163.  Fawcett,  H.  S.,  Scaby  bark  of 
Citrus.  Fla.  Agr.  Exp.  Sta.  Bui.  98.  1909.  164.  Powell,  G.  H., 
The  decay  of  oranges  while  in  transit  from  California.  U.  S.  Dept. 
Agr.,  B.  P.  I.  Bui.  123.  1908.  165.  Coit,  J.  E.,  and  Hodgson, 
R.  W.,  The  June  drop  of  Washington  navel  oranges.  Cal.  Agr. 
Exp.  Sta.  Bui.  290.  1918.  166.  Matz,  J.,  Some  diseases  of  the 
fig.  Fla.  Agr.  Exp.  Sta.  Bui.  149.  1918.  167.  Johnson,  R.  J., 
The  history  and  cause  of  the  cocoanut  bud-rot.  U.  S.  Dept.  Agr., 
B.  P.  I.  Bui.  228.  1912.  168.  Hodgson,  R.  W.,  Black  smut  of 
figs.  Mo.  Bui.  of  St.  Comm.  of  Hort.  (Cal.)  7:  188.  1918.  169. 
Rorer,  J.  B.,  The  anthracnose  of  the  mango.  Bui.  Dept.  Agr. 
Trinidad  and  Tobago  I4:  164.  1915.  170.  Swingle,  W.  T.,  and 
Webber,  H.  J.,  The  principal  diseases  of  citrus  fruits  in  Florida. 
U.  S.  Dept.  Agr.  Div.  Veg.  Phys.  and  Path.  Bui.  8.  1896.  171. 
Webber,  H.  J.,  Sooty  mold  of  the  orange  and  its  treatment.  U.  S. 
Dept.  Agr.  Div.  Veg.  Phys.  and  Path.  Bui.  13.  1897.  172.  Tauben- 
haus,  J.  J.,  Diseases  of  truck  crops.  E.  P.  Dutton  &  Co.  1918. 
173.  Halsted,  B.  D.,  The  asparagus  rust,  its  treatment  and  natural 
enemies.  N.  J.  Agr.  Exp.  Sta.  Bui.  129.  1898.  174.  Norton,  J.  B., 
Washington  asparagus.  U.  S.  Dept.  Agr.,  B.  P.  I.,  Cotton,  truck, 
etc.  Feb.,  1919.  175.  Smith,  R.  E.,  Asparagus  and  asparagus  rust 
in  California.  Cal.  Agr.  Exp.  Sta.  Bui.  165.  1905.  176.  Sirrine, 
F.  A.,  Spraying  for  asparagus  rust.  N.  Y.  (Geneva)  Agr.  Exp.  Sta. 
Bui. /5S.- 251.  1900.  177.  Jackson,  H.  S.,  Diseases  of  field  crops  in 
Delaware.  Del.  Agr.  Exp.  Sta.  Bui.  83.  1907.  178.  Burkholder, 
W.  H.,  The  production  of  an  anthracnose-resistant  white  marrow 
bean,  Phytop.  5.- 353.  1918.  179.  Barrus,  M.  F.,  An  anthracnose- 
resistant  red  kidney  bean.  Phytop.  5:  303.  1915.  Idem.  8:  589. 
1918.  180.  Whetzel,  H.  H.,  Bean  anthracnose.  N.  Y.  (Cornell) 
Agr.  Exp.  Sta.  Bui.  255.  1908.  181.  Beach,  S.  A.,  Some  bean 
diseases.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  48.  1892.  182. 
Duggar,  B.  M.,  and  Stewart,  F.  C,  The  sterile  fungus  Rhizoctonia. 
N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  186.  1901.  183.  Hedgcock,  G. 
G.,  A  note  on  Rhizoctonia.    Sc.  n.  s.  19:  268.    1904.    184.  Halsted, 


Bibliography  475 

B.  D.,  Bean  diseases  and  their  treatments.  N.  J.  Agr.  Exp.  Sta. 
Bui.  151.  1901.  185.  Thaxter,  R.,  A  new  American  Phytoph- 
thora.  Bot.  Gaz.  I4:  273.  1889.  186.  Reddick,  D.,  and  Stewart, 
V.  B.,  Varieties  of  beans  susceptible  to  mosaic.  Phytop.  8:  530. 
1918.  187.  Miles,  L.  E.,  Some  diseases  of  economic  plants  in 
Porto  Rico.  Phytop.  7:  345.  1917.  188.  Harter,  L.  L.,  Podblight 
of  the  lima  bean  caused  by  Diaporthe  phaseolorum.  Jour.  Agr. 
Res.  11:  473.  1917.  189.  Macmillan,  H.  G.,  Sunscald  of  beans. 
Jour.  Agr.  Res.  13:  647.  1918.  190.  McClintock,  J.  A.,  Sclerotinia 
blight.  Va.  Truck  Exp.  Sta.  Bui.  ^0.  1916.  191.  Townsend,  C.  0., 
Leaf  spot.  IT.  S.  Dept.  Agr.  Farms'.  Bui.  618.  1914.  192.  Hal- 
sted,  B,  D.,  Some  fungous  diseases  of  beets.  N.  J.  Agr.  Exp.  Sta. 
Bui.  ^07.  1895.  193.  Pool,  V.  W.,  and  McKay,  M.  B.,  The  control 
of  the  sugar-beet  leaf-spot.  U.  S.  Dept.  Agr.,  B.  P.  I.  Cir.  121. 
1913.  194.  Duggar,  B.  M.,  and  Stewart,  F.  C,  The  sterile  fungus 
Rhizoctonia.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  186.  1901. 
195.  BoUey,  H.  L.,  Potato  scab  and  possibilities  of  prevention. 
N.  Dak.  Agr.  Exp.  Sta.  Bui.  4.  1891.  196.  Metcalf,  H.,  A  soft  rot 
of  the  sugar  beet.  Neb.  Agr.  Exp.  Sta.  Rept.  17:  69.  1904.  197. 
Brown,  N.  A.,  A  new  bacterial  disease  of  nasturtiums.  Sc.  n.  s.  29; 
915.  1909.  198.  Hedgcock,  G.  G.,  Proof  of  the  identity  of  Phoma 
and  Phyllosticta  on  the  sugar  beet.  Jour.  Myc.  10:  2.  1904.  199. 
Smith,  R.  E.,  and  Boncquet,  P.  A.,  Connection  of  a  bacterial  or- 
ganism with  curly  leaf  of  the  sugar  beet.  Phytop.  5:  335.  1915. 
200.  Shaw,  H.  B.,  The  curly  top  of  beets.  U.  S.  Dept.  Agr.,  B.  P.  I. 
Bui.  181.  1910.  201.  Ball,  E.  D.,  The  beet  leaf-hopper  and  the 
curly-leaf  disease  that  it  transmits.  Utah  Agr.  Exp.  Sta.  Bui.  lo5. 
1917.  202.  Stewart,  F.  C,  Leaf-scorch  of  the  sugar-beet,  cherry, 
cauliflower,  and  maple.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  162. 
1899.  203.  Shaw,  H.  B.,  Control  of  the  sugar-beet  nematode. 
IT.  S.  Dept.  Agr.  Farms'.  Bui.  772.  1916.  204.  Edson,  H.  A., 
Seedling  diseases  of  sugar-beets  and  their  relation  to  root-rot  and 
crown-rot.  Jour.  Agr.  Res.  4:  135  and  279.  1918.  205.  Stevens, 
F.  L.,  and  Wilson,  G.  W.,  Rhizoctonia  on  buckwheat.  Sc.  n.  s. 
33:  943.  1911.  206.  Russell,  H.  L.,  A  leaf-rot  of  cabbage.  Proc. 
Amer.  Assoc.  Adv.  Sci.  1895.  1896.  207.  Russell,  H.  L.,  A  bac- 
terial rot  of  cabbage  and  allied  plants.    Wis.  Agr.  Exp.  Sta.  Bui.  65. 


476  Bibliography 

1898.  208.  Harter,  L.  L.  and  Jones,  L.  R.,  Cabbage  diseases.  U.S. 
Dept.Agr.  Farms'.  Bui.  .9^.5.  1918.  209.  Lutman,  B.  F.,  Studies  in 
club-root.  Vt.  Agr.  Exp.  Sta.  Bui.  175.  1913.  210.  Cunningham, 
G.  C,  Studies  in  club-root.  Vt.  Agr.  Exp.  Sta.  Bui.  185.  1914. 
211.  Stewart,  F.  C,  Prevention  of  cabbage  club-root.  N.  Y. 
(Geneva)  Agr.  Exp.  Sta.  Rept.  I4:  528.  1896.  212.  Hedgcock,  G. 
G.,  A  disease  of  cauliflower  and  cabbage  caused  by  Sclerotinia. 
Mo.  Bot.  Card.  Rept.  16:  149.  1905.  213.  Henderson,  M.  P.,  The 
black-leg  disease  of  cabbage  caused  by  Phoma  lingam  (Tode) 
Desmaz.  Phytop.  8:  379.  1918.  214.  Manns,  T.  F.,  Two  recent 
important  cabbage  diseases  in  Ohio.  Ohio  Agr.  Exp.  Sta.  Bui.  238. 
1911.  215.  McCulloch,  L.,  A  spot  disease  of  cauliflower.  U.  S. 
Dept.  Agr.  Bui.  225.  1911.  216.  Orton,  W.  A.,  Watermelon 
diseases.  U.  S.  Dept.  Agr.  Farms'.  Bui.  821.  1917.  217.  BUnn, 
P.  K.,  A  rust  resistant  canteloupe.  Colo.  Agr.  Exp.  Sta.  Bui.  104. 
1905.  218.  Giddings,  N.  J.,  A  bacterial  rot  of  the  muskmelon.  Sc. 
n.  s.  29:  911.  1909.  219.  Giddings,  N.  J.,  A  bacterial  soft-rot  of 
muskmelon  caused  by  Bacillus  melonis  n.  sp.  Vt.  Agr.  Exp.  Sta. 
Bui.  148.  1910.  220.  Grossenbacher,  J.  G.,  A  mycosphserella  wilt 
of  melons.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Tech.  Bui.  9.  1909. 
221.  Harding,  H.  A.,  Jones,  L.  R.,  and  Morse,  W.  J.,  The  bacterial 
soft-rots  of  certain  vegetables.  N.  Y.  (Geneva)  Agr.  Exp.  Sta. 
Tech.  Bui.  11.  1910.  222.  Jones,  L.  R.,  A  soft-rot  of  carrot  and 
other  vegetables.  Vt.  Agr.  Exp.  Sta.  Rept.  13:  299.  1901.  223. 
Harrison,  F.  C,  A  bacterial  disease  of  cauliflower  (Brassica  oleracea) 
and  allied  plants.  Ont.  A.  C.  &E.  F.  Bui.  iS7.  1904.  224.  Stevens, 
H.  E.,  Gray  mold  of  castor  beans.  Fla.  Agr.  Exp.  Sta.  Press  Bui. 
296.  1918.  225.  Lamson-Scribner,  F.,  Celery  leaf  blight.  U.  S. 
Dept.  Agr.  Rept.  for  1886.  117.  226.  Coons,  G.  H.,  and  Levin,  E., 
The  septoria  leaf-spot  disease  of  celery  or  celery  blight.  Mich.  Agr. 
Exp.  Sta.  Sp.  Bui.  77.  1916.  227.  Chubb,  C,  Studies  on  club-root 
of  crucifers.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  387.  1917.  228. 
Harding,  H.  A.  et  al.,  VitaUty  of  the  cabbage  black  rot  germ  on 
cabbage  seed.     N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  251.     1904. 

229.  Jones,  L.  R.,  and  Oilman,  J.  C,  The  control  of  cabbage  yellows 
through  disease  resistance.    Wis.  Agr.  Exp.  Sta.  Res.  Bui.  38.    1915. 

230.  Austin,  C.  F.,  and  White,  T.  H.,  Second  report  on  the  cause  of 


Bibliography  477 

pithiness  in  celery.  Md.  Agr.  Exp.  Sta.  Bui.  93.  1904.  231.  Stew- 
art, F.  C,  The  downy  mildew  of  the  cucumber.  N.  Y.  (Geneva) 
Agr.  Exp.  Sta.  Bui.  119.  1897.  232.  Gardner,  M.  W.,  Anthracnose 
of  cucurbits.  U.  S.  Dept.  Agr.  Bui.  727.  1918.  233.  Humphrey, 
J.  E.,  The  powdery  mildew  of  the  cucumber.  Mass.  Agr.  Exp.  Sta. 
Rept.  9:  222.  1892.  234.  Arthur,  J.  C,  A  fungous  disease  of  the 
cucumber.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Rept.  6:  316.  1887. 
235.  Burger,  0.  F.,  Cucumber  rot.  Fla.  Agr.  Exp.  Sta.  Bui.  121. 
1914.  236.  Gilbert,  W.  W.,  and  Gardner,  M.  W.,  Seed  treatment 
control  and  over-wintering  of  cucumber  angular  leaf-spot.  Phytop. 
8:  229.  1918.  237.  Jagger,  I.  C.^  Mosaic  diseases  of  cucurbits 
(abstract).  Phytop.  8:  74.  1918.  238.  Doolittle,  S.  P.,  and 
Williams,  W.,  Further  notes  on  cucumber  mosaic  diseases  (abstract). 
Phytop.  8:  77.  1918.  239.  Humphrey,  J.  E.,  Diseases  of  the  cu- 
cumber plant.  Mass.  Agr.  Exp.  Sta.  Rept.  1892:  227.  1893.  240. 
Orton,  W.  A.,  Spraying  for  cucumber  and  melon  diseases.  U.  S. 
Dept.  Agr.  Farms'.  Bui.  231.  1908.  241.  Meier,  F.  C,  Melon 
stem-end  rot.  Jour.  Agr.  Res.  6:  149.  1916.  242.  Osner,  G.  A., 
Stemphylium  leaf-spot  of  cucumbers.  Jour.  Agr.  Res.  13:  295. 
1918.  243.  Harter,  L.  L.,  Fruit-rot,  leaf -spot,  and  stem-blight  of 
the  egg  plant  caused  by  Phomopsis  vexans.  Jour.  Agr.  Res.  2:  331. 
1914.  244.  Whetzel,  H.  H.,  et  al.,  Ginseng  diseases  and  their  con- 
trol. U.  S.  Dept.  Agr.  Farms'.  Bui.  736.  1916.  245.  Whetzel, 
H.  H.,  and  Rosenbaum,  J.,  The  diseases  of  ginseng  and  their  control. 
U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  ^.50.  1912.  246.  Reed,  H.  S.,  Three 
fungous  diseases  of  the  cultivated  ginseng.  Mo.  Agr.  Exp.  Sta.  Bui. 
69.  1905.  247.  Rosenbaum,  J.,  Phytophthora  disease  of  ginseng. 
N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  363.  1915.  248.  Stevens,  F. 
L.,  A  serious  lettuce  disease  and  a  method  of  control.  N.  C.  Agr. 
Exp.  Sta.  Tech.  Bui.  §.  1911.  249.  Brandes,  E.  W.,  Anthracnose  of 
lettuce  caused  by  Marssonina  panattoniana.  Jour.  Agr.  Res.  13: 
261.  1918.  250.  Brown,  N.  A.,  Some  bacterial  diseases  of  lettuce. 
Jour.  Agr.  Res.  13:  367.  1918.  251.  Selby,  A.  D.,  Diseases  of 
lettuce.  Ohio  Agr.  Exp.  Sta.  Bui.  73.  1896.  252.  Veihmeyer, 
F.  J.,  The  Mycogone  disease  of  mushrooms  and  its  control.  U.  S. 
Dept.  Agr.  Bui.  127.  1914.  253.  Carpenter,  C.  W.,  Wilt  diseases  of 
okra  and  the  Verticillium  wilt  problem.    Jour.  Agr.  Res.  12:  529. 


478  Bibliography 

1918.  254.  Tolaas,  A.  G.,  A  bacterial  disease  of  cultivated  mush- 
rooms. Phytop.  5.- 51.  1915.  255.  Stone,  Geo.  E.,  The  control  of 
onion  smut.  Mass.  (Amherst)  Agr.  Exp.  Sta.  Cir.  41  •  1914- 
256.  Thaxter,  R.,  The  "smut"  of  onions.  Ct.  Agr.  Exp.  Sta.  Rept. 
1889:  129.  1900.  257.  Selby,  A.  D.,  The  prevention  of  onion  smut. 
Ohio  Agr.  Exp.  Sta.  Bui.  131.  1900.  258.  Thaxter,  R.,  Report  of 
Roland  Thaxter,  Mycologist.  Conn.  Agr.  Exp.  Sta.  Rept.  1889:  127. 
1890.  259.  Whetzel,  H.  H.,  Onion  blight.  N.  Y.  (Cornell)  Agr. 
Exp.  Sta.  Bui.  218.  1904.  260.  Stewart,  F.  C,  A  bacterial  rot  of 
onions.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  164.  1899.  261. 
Munn,  M.  T.,  Neck-rot  disease  of  onions.  N.  Y.  (Geneva)  Agr. 
Exp.  Sta.  Bui.  457.  1917.  262.  Von  Pelt,  W.,  Black  mold  of  onions. 
Ohio  Agr.  Exp.  Sta.  Mo.  Bui.  2.  No.  5.  1917.  263.  Taubenhaus, 
J.  J.,  Pink-rot  of  onions.  Sc.  n.  s.  49:  218.  1919.  264.  Selby,  A. 
D.,  The  blighting  of  field  and  garden  peas.  Ohio  Agr.  Exp.  Sta. 
Bui.  173.  1906.  265.  Sackett,  W.  G.,  A  bacterial  stem  bhght  of 
field  and  garden  peas.  Colo.  Agr.  Exp.  Sta.  Bui.  218.  1916.  266. 
Lamson-Scribner,  F.,  Diseases  of  the  Irish  potato.  Tenn.  Agr. 
Exp.  Sta.  Bui.  2:  2.  1889.  267.  Orton,  W.  A.,  The  development  of 
farm  crops  resistant  to  di.sease.  IT.  S.  Dept.  Agr.  Yearbook.  453. 
1908.  268.  Melhus,  I.  E.,  Germination  and  infection  with  the 
fungus  of  the  late  blight  of  potato  (Phytophthora  infestans).  Wis. 
Agr.  Exp.  Sta.  Res.  Bui.  37.  1915.  269.  Jones,  L.  R.,  Disease 
resistance  of  potatoes.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  87.  1905. 
270.  Jones,  L.  R.,  and  Morse,  W.  J.,  Report  of  the  botanists.  Vt. 
Agr.  Exp.  Sta.  Rept.  16:  163.  1902-1903.  271.  Stewart,  F.  C, 
et  al.,  Potato  spraying  experiments  in  1906.  N.  Y.  (Geneva)  Agr. 
Exp.  Sta.  Bui.  290:  240.  1907.  272.  Lutman,  B.  F.,  and  Cunning- 
ham, G.  C,  Potato  scab.  Vt.  Agr.  Exp.  Sta.  Bui.  I84.  1914.  273. 
Thaxter,  R.,  The  potato  scab.  Ct.  State  Agr.  Exp.  Sta.  Rept.  14- 
81.  1891.  274.  Norton,  J.  B.  S.,  Irish  potato  diseases.  Md.  Agr. 
Exp.  Sta.  Bui.  108:  67.  1906.  275.  Morse,  W.  J.,  and  Shapavalov, 
M.,  The  Rhizoctonia  disease  of  potatoes.  Me.  Agr.  Exp.  Sta.  Bui. 
230.  1914.  276.  Melhus,  T.  E.,  Powdery  scab  (Spongospora  sub- 
terranea)  of  potatoes.  U.  S.  Dept.  Agr.  Bui.  82.  1914.  277. 
Spaulding,  P.,  and  Field,  E.  C,  Two  dangerous  imported  plant 
diseases.    U.  S.  Dept.  Agr.  Farms'.  Bui.  489.    1912.    278.  Edson, 


Bibliography  479 

H.  A.,  and  Shapavalov,  M.,  Potato-stem  lesions.  Jour.  Agr.  Res. 
14:  213.  1918.  279.  Rands,  R.  D.,  Early-blight  of  potato  and 
related  plants.  Wis.  Agr.  Exp.  Sta.  Res.  Bui.  42.  1917.  280. 
Smith,  E.  F.,  and  Swingle,  D.  B.,  The  dry  rot  of  potatoes.  U.  S. 
Dept.Agr.B.P.  T.,Bul.55.  1904.  281.  Jones,  L.  R.,  and  Pomeroy, 
C.  S.,  The  leaf  blotch  disease  of  the  potato  caused  by  Cercospora 
concors.  Vt.  Agr.  Exp.  Sta.  Rept.  19:  236.  1907.  282.  Orton, 
W.  A.,  Potato  diseases  in  San  Joaquin  county,  California.  U.  S. 
Dept.  Agr.,  B.  P.  I.  Cir.  23.  1909.  283.  Jones,  L.  R.,  Certain 
potato  diseases  and  their  remedies.  Vt.  Agr.  Exp.  Sta.  Bui.  72. 
1899.  284.  Morse,  W.  J.,  Control  of  blackleg  disease  of  the  potato. 
Me.  Agr.  Exp.  Sta.  Bui.  lOJ^.  1911.  285.  Morse,  W.  J.,  Studies 
upon  the  blackleg  disease  of  potato.  Jour.  Agr.  Res.  8:  79.  1917. 
286.  Murphy,  P.  A.,  War  Emergency  Board  Rept.  Aug.  16-17, 
191S.  13.  287.  Wortley,  E.  J.,  War  Emergency  Board  Rept. 
Aug.  16-17.  1918.  5.  288.  Orton,  W.  A.,  Potato  wilt,  leaf-roll, 
and  related  diseases.  U,  S.  Dept.  Agr.  Bui.  64.  1914.  289.  Bar- 
tholomew, E.  T.,  Black  heart  of  potatoes.    Phytop.  3:  180.    1913. 

290.  Stewart,  F.  C,  and  Mix,  A.  J.,  Black  heart  and  the  aeration  of 
potatoes  in  storage.    N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  426.    1917. 

291.  Lutman,  B.  F.,  Twenty  years'  spraying  for  potato  diseases  and 
the  weather.  Vt.  Agr.  Exp.  Sta.  Bui.  159.  1911.  292.  Stewart, 
F.  C,  et  al.,  Potato  spraying  experiments  1902-1911.  N.  Y.  (Gen- 
eva) Agr.  Exp.  Sta.  Bui.  349.  1911.  293.  Orton,  W.  A.,  Selection 
and  treatment  of  seed  potatoes  to  avoid  disease.  IT.  S.  Dept.  Agr., 
B.  P.  I.  Cir.  3.  C.  T.  &  F.  C.  D.  1918.  294.  Stevens,  F.  L.,  Tavo 
Illinois  rhubarb  diseases.  111.  Agr.  Exp.  Sta.  Bui.  213.  1919. 
295.  McClintock,  J.  A.,  and  Smith,  L.  R.,  True  nature  of  spinach 
blight  and  the  relation  of  insects  to  its  transmission.  Jour.  Agr. 
Res.  14:  1.  1918.  296.  Zundel,  G.  L.,  Wheat  smut  control.  13th 
Ann.  Conv.  Washington  Grain  Growers,  etc.,  Asso.,  Jan.,  1919.  297. 
Halsted,  B.  D.,  Identity  of  anthracnose  of  the  bean  and  watermelon. 
N.  J.  Agr.  Exp.  Sta.  Rept.  11:  351.  1890.  298.  Halsted,  B.  D., 
Some  fungous  diseases  of  the  spinach.  N.  J.  Agr.  Exp.  Sta.  Bui.  70. 
1890.  299.  Harter,  L.  L.,  Sweet  potato  diseases.  U.  S.  Dept.  Agr. 
Farms'.  Bui.  714.  1916.  300.  Waite,  M.  B.,  Sweet  Potatoes.  Cy- 
clopedia of  Amer.  Agr.  ^.- 622.    1907.    301.  Elliott,  J.  A.,  The  sweet 


480  Bibliography 

potato  "soil  rot"  or  "pox,"  a  slime  mold  disease,  Del.  Agr.  Exp. 
Sta.  Bui.  114.  1916.  302.  Harter,  L.  L.,  The  foot  rot  of  the  sweet 
potato.  Jour.Agr.  Res.  ^.-251.  1914.  303.  Halsted,  B.  D.,  Exper- 
iments with  sweet  potatoes.  N.  J.  Agr.  Exp.  Sta.  Rept.  350.  1898. 
304.  Clendenin,  Ida,  Lasiodiplodia  E.  &  E.  n.  gen.  Bot.  Gaz.  21: 
92.  1896.  305.  Taubenhaus,  J.  J.,  Soil-stain,  or  scurf  of  the  sweet 
potato.  Jour.  Agr.  Res.  5;  995.  1916.  306.  Wolf,  F.  A.,  and  Foster, 
A.  C,  Tobacco  wildfire.  Jour.  Agr.  Res.  12:  449.  1918.  307. 
Stevens,  F.  L.,  The  Granville  tobacco  wilt.  N.  C.  Agr.  Exp.  Sta. 
Press  Bui.  11.  1903.  308.  Sturgis,  W.  C.,  On  a  destructive  fungous 
disease  of  tobacco  in  South  Carolina.  Conn.  State  Agr.  Exp.  Sta. 
Rept.  20:  273.  1896.  309.  Smith,  E.  F.,  A  dangerous  tobacco 
disease.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  I4I.  part  II.  1908.  310. 
Garner,  W.  W.,  et  al.,  The  control  of  tobacco  wilt  in  the  flue-cured 
district.  U.  S.  Dept.  Agr.  Bui.  562.  1917.  311.  Clinton,  G.  P., 
Notes  on  fungous  diseases  for  1905.  Conn.  State  Agr.  Exp.  Sta. 
Rept.  276.  1905.  312.  Chapman,  G.  H.,  Mosaic  disease  of  tobacco. 
Mass.  (Amherst)  Agr.  Exp.  Sta.  Bui.  175.  1917.  313.  Allard. 
H.  A.,  The  mosaic  disease  of  tobacco.  U.  S.  Dept.  Agr.  Bui.  40- 
1914.  314.  Smith,  E.  F.,  A  bacterial  disease  of  the  tomato,  egg- 
plant, and  Irish  potato.  U.  S.  Dept.  Agr.  Div.  Veg.  Phys.  &  Path- 
Bul.  12.  1896.  315.  Smith,  R.  E.,  Tomato  diseases  in  California, 
Cal.  Agr.  Exp.  Sta.  Bui.  175.  1906.  316.  Levin,  E.,  The  leaf- 
spot  disease  of  tomato.  Mich.  Agr.  Exp.  Sta.  Tech.  Bui.  25.  1916. 
317.  Jamieson,  C.  O.,  Phoma  destructiva,  the  cause  of  a  fruit-rot 
of  the  tomato.  Jour.  Agr.  Res.  4:  1.  1915.  318.  Selby,  A.  D., 
Studies  in  potato  rosette.  Ohio  Agr.  Exp.  Sta.  Bui.  I45.  1903. 
319.  Pammel,  L.  H.,  Rutabaga  rot.  la.  Agr.  Exp.  Sta.  Bui.  27. 
1895.  320.  Clinton,  G.  P.,  North  American  Ustilaginese.  Proc. 
Boston  Soc.  Nat.  Hist.  31:  334.  1904.  321.  Bolley,  H.  L.,  New 
studies  upon  the  smut  of  wheat,  oats,  and  barley.  N.  D.  Agr. 
Exp.  Sta.  Bui.  27.  1897.  322.  Arthur,  J.  C,  Rapid  method  of  re- 
moving smut  from  seed  oats.    Ind.  Agr.  Exp.  Sta.  Bui.  103.    1905. 

323.  Haskell,  R.  J.,  The  spray  method  of  applying  concentrated 
formaldehyde  solution  in  the  control  of  oat  smut.    Phytop.  7.  1917. 

324.  Humphrey,  H.  B.,  and  Potter,  A.  A.,  Cereal  smuts  and  the 
disinfection  of  seed  grain.     U.  S.  Dept.  Agr.  Farms'.  Bui.  S3S. 


Bibliography  481 

1918.  325  Melchers,  L.  E.,  Smuts  of  grain  and  forage  crops  in 
Kansas.  Kan.  Agr.  Exp.  Sta.  Bui.  210.  1916.  326.  Freeman, 
E.  M.,  and  Johnson,  E.  C,  The  loose  smuts  of  barley  and  wheat. 
U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  152.  1909.  327.  War  Emergency 
Board  of  Plant  Pathologists.  Aug.,  1918.  328.  Carleton,  M.  A., 
Cereal  rusts  of  the  United  States.  U.  S.  Dept.  Agr.,  Div.  Veg.  Phys. 
&  Path.  Bui.  16:  19.  1899.  329.  Selby,  A.  D.,  and  Manns,  T.  F., 
Studies  in  diseases  of  cereals  and  grasses.  Ohio  Agr.  Exp.  Sta.  Bui. 
203.  1909.  330.  Jones,  L.  R.,  Johnson,  A.  G.,  and  Reddy,  C.  S., 
Bacterial  blight  of  barley.  Jour.  Agr.  Res.  11:  625.  1917.  331. 
Pammel,  L.  H.,  King,  C.  M.,  and  Bakke,  A.  L.,  Two  barley  blights. 
la.  Agr.  Exp.  Sta.  Bui.  116.  1910.  332.  Clinton,  G.  P.,  Broom 
corn  smut.  111.  Agr.  Exp.  Sta.  Bui.  47.  1897.  333.  Arthur,  J.  C, 
and  Stuart,  W.,  Corn  smut.  Ind.  Agr.  Exp.  Sta.  Rept.  12:  84. 
1900.  334.  Burrill,  T.  J.,  and  Barrett,  J.  T.,  Ear  rots  of  corn.  111. 
Agr.  Exp.  Sta.  Bui.  133.  1909.  335.  Arzberger,  E.  G.,  Cob  rot  of 
corn.  Ohio  Agr.  Exp.  Sta.  Bui.  265.  1913.  336.  Stewart,  F.  C, 
A  bacterial  disease  of  sweet  corn.  N.  Y.  (Geneva)  Agr.  Exp.  Sta. 
Bui.  130.  1897.  337.  Tisdale,  W.  H.,  Physoderma  disease  of  corn. 
Jour.  Agr.  Res.  16:  137.  1919.  338.  Stewart,  F.  C,  Blight  of  corn 
leaves.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Rept.  15:  452.  1897. 
339.  Thaxter,  R.,  Report  of  Plant  Pathologist,  Conn.  State  Agr. 
Exp.  Sta.  Rept.  13:  171.  1889.  340.  Smith,  E.  F.,  Bacteria  in 
relation  to  plant  disease  II.  Pub.  Carnegie  Inst.  Washington, 
1911.  341.  Idem,  3.  1914.  342.  Jones,  L.  R.,  et  al,  Investiga- 
tions of  the  potato  fungus,  Phytophthora  infestans.  U.  S.  Dept. 
Agr.,  B.  P.  I.  Bui.  245.  1912.  343.  Arthur,  J.  C,  Smut  of  oats. 
N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Rept.  3.  1884.  344.  Plumb,  C.  S., 
Smut  experiments  with  oats.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Rept. 
5:  109.  1886.  345.  Kellerman,  W.  A.,  and  Swingle,  W.  T.,  Report 
on  the  loose  smuts  of  cereals.    Kan.  Agr.  Exp.  Sta.  Rept.  213.    1889. 

346.  Galloway,  B.  T.,  and  Southworth,  E.  A.,  Preliminary  notes 
on  a  new  and  destructive  oat  disease.    Jour.  Myc.  6:  72.     1891. 

347.  Manns,  T.  F.,  The  blade  blight  of  oats.  Ohio  Agr.  Exp.  Sta. 
Bui.  210.  1909.  348.  Fulton,  H.  R.,  Diseases  affecting  rice.  La. 
Agr.  Exp.  Sta.  Bui.  105.  1908.  349.  Metcalf,  Haven,  A  pre- 
liminary report  on  the  blast  of  rice.    S.  C.  Agr.  Exp.  Sta.  Bui.  121. 


482  Bibliograpluj 

1906.  350.  Anderson,  A.  P.,  Rice  blast  and  a  new  smut  on  the  rice 
plant.  S.  C,  Agr.  Exp.  Sta.  Bui.  4I.  1899.  351.  Cobb,  N.  A., 
Fungus  maladies  of  the  sugar-cane.  Hawaiian  Sug.  PI.  Assn.  Bui.  5. 
352.  Reed,  G.  M.,  The  powdery  mildews  of  Avena  and  Triticum. 
Mo.  Agr.  Exp.  Sta.  Res.  Bui.  23.  1916.  353.  Heald,  F.  D.,  Report 
on  the  plant  diseases  prevalent  in  Nebraska  during  the  season  of 
1905.  Neb.  Agr.  Exp.  Sta.  Rept.  19:  46.  1906.  354.  Selby,  A.  D., 
Some  diseases  of  wheat  and  oats.  Ohio  Agr.  Exp.  Sta.  Bui.  97. 
1898.  355.  Smitli,  E.  F.,  A  new  disease  of  wheat.  Jour.  Agr.  Res. 
10:  51.  1917.  356.  Smith,  E.  F.,  In  the  Plant  Disease  Bulletin  2: 
N0.6,  98,  issued  by  the  Plant  Disease  Survey..  1918.    357.  Gilbert, 

A.  H.,  and  Bennet,  C.  W.,  Sclerotinia  trifoliorum,  the  cause  of 
stem-rot  of  clovers  and  alfalfa.  Phytop.  7:  432.  1917.  358.  Jones, 
F.  R.,  The  yellow-leaf  blotch  of  alfalfa  caused  by  the  fungus  Pyren- 
opeziza  medicaginis.  Jour.  Agr.  Res.  13:  307.  1918.  359.  Stewart, 
F.  C.,  French,  G.  T.,  and  Wilson,  J.  K.,  Troubles  of  alfalfa  in  New 
York,  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  305.  1908.  360.  Bain, 
S.  M.,  and  Essary,  S.  H.,  A  preliminary  note  on  clover  diseases  in 
Tennessee.  Sc.  n.  s.  22:  503.  1905.  361.  Paddock,  W.,  A  new 
alfalfa  disease.  Colo.  Agr.  Exp.  Sta.  Press  Bui.  28.  1906.  362. 
Sackett,  W.  G.,  A  bacterial  disease  of  alfalfa.  Colo.  Agr.  Exp.  Sta. 
Bui.  158.     1910.    363.  Field,  E.  C,  Ms.  Article.    U.  S.  Dept.  Agr., 

B.  P.  I.  364.  Hillman,  F.  H.,  Dodder  in  relation  to  farm  seeds. 
U.  S.  Dept.  Agr.  Farms'.  Bui.  306.  1907.  365.  Bain,  S.  M.,  and 
Essary,  S.  H.,  Selection  for  disease-resistant  clover.  Tenn.  Agr. 
Exp.  Sta.  Bui.  75.  1906.  366.  Orton,  W.  A.,  Some  diseases  of  the 
cowpea.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  17.  1902.  367.  Brown, 
H.  B.,  and  Ranck,  E.  M.,  Forage  poisoning  due  to  Claviceps  paspali 
on  Paspalum.  Miss.  Agr.  Exp.  Sta.  Tech.  Bui.  6.  1915.  368. 
Osner,  G.  A.,  Leaf  smut  of  timothy.  N.  Y.  (Cornell)  Agr.  Exp. 
Sta.  Bui.  381.  1916.  369.  Lewis,  A.  C,  Cotton  wilt  in  Georgia, 
Ga.  St.  Bd.  Ent.  Bui.  40.  1915.  370.  Barre,  H.  W.,  Cotton  an- 
thracnose.  S.  C.  Agr.  Exp.  Sta.  Bui.  I64.  1912.  371.  Rolfs,  F.  M., 
Cotton  anthracnose.  Okla.  Agr.  Exp.  Sta.  Cir.  40.  1916.  372. 
Shear,  C.  L.,  and  Miles,  Geo.  F.,  The  control  of  Texas  root-rot  of 
cotton.  U.  S.  Dept.  Agr.,  B.  P.  L  Bui.  102.  Part  V.  1907.  373. 
Shear,  C.  L.,  and  Miles,  Geo.  F.,  Texas  root-rot  of  cotton.    U.  S. 


Bibliography  483 

Dept.  Agr.,  B.  P.  I.  Cir.  9.  1908.  374.  Rolfs,  F.  M.,  Angular  leaf- 
spot  of  cotton.  S.  C.  Agr.  Exp.  Sta.  Bui.  I84.  1915.  375.  Edger- 
ton,  C.  W.,  The  rots  of  the  cotton  boll.  La.  Agr.  Exp.  Sta.  Bui.  137. 
1912.  376.  Bolley,  H.  L.,  Flax  wilt  and  flax  sick  soil.  N.  Dak. 
Agr.  Exp.  Sta.  Bui.  50.  1901.  377.  Charles,  V.  K.,  A  fungous 
disease  of  hemp.  Jour.  Agr.  Res.  3:  81.  1915.  378.  Rankin,  W. 
H.,  Manual  of  tree  diseases.  The  Macmillan  Co.  1918.  379. 
Schrenk,  H.  v.,  Fungous  diseases  of  forest  trees.  U.  S.  Dept.  Agr. 
Yearbook  1900:  199.  1901.  380.  Abbott,  F.  H.,  The  red-rot  of 
conifers.  Vt.  Agr.  Exp.  Sta.  Bui.  L9^  1915.  381.  Kauffman,  C. 
H.,  The  Agaricaceae  of  Michigan.  Mich.  Geol.  and  Biol.  Surv.  Pub. 
36.  Biol.  ser.  5.  1918.  382.  Overholts,  L.  0.,  The  Polyporaceaj  of 
the  middle-western  United  States.  Wash.  Uni.  Studies  3.  Part  1. 
No.  1.  1915.  383.  Hard,  M.  E.,  The  Mushroom.  The  Ohio 
Library  Co.  1908.  384.  Mcllvaine,  C,  One  thousand  American 
fungi.  The  Boden  Merrill  Co.  1900.  385.  Atkinson,  G.  F.,  Mush- 
rooms. Ithaca,  N.  Y.  1901.  386.  Marshall,  N.,  The  mushroom 
book.  Doubleday  Page  &  Co.  1905.  387.  Moffatt,  W.  S.,  The 
higher  fungi  of  the  Chicago  region.  Chicago  Academy  of  Sciences. 
1909.  388.  Schrenk,  H.  v..  Some  diseases  of  New  England  conifers. 
U.  S.  Dept.  Agr.,  Div.  Veg.  Phys.  &  Path.  Bui.  25.  1900.  389. 
Schrenk,  H.  v.,  and  Spaulding,  P.,  Diseases  of  deciduous  forest 
trees.  U.  S.  Dept.  Agr.,  B.  P.  L  Bui.  I49.  1909.  390.  Stevens, 
F.  L.,  The  fungi  which  cause  plant  disease.    Macmillan  Co.    1913. 

391.  Duggar,  B.  M.,  Fungous  diseases  of  plants.    Ginn  &  Co.    1909. 

392.  Saccardo,  P.  A.^  Sylloge  fungorum  omnium  hucusque  cogni- 
torium,  Pavia.  R.  Friedlander  &  Sohn.  1882.  393.  Engler  and 
Prantl,  Natiirlichen  Pflanzenfamilien.  Wm.  Engelmann.  1897. 
394.  Rabenhorst,  Kryptogamen  Flora  von  Deutschland  Oesterrich 
und  der  Schweiz.  1887.  395.  Sherfesee,  W.  F.,  Wood  preservation 
in  the  United  States.  U.  S.  Forestry  Service  Bui.  78.  1909.  396. 
Hunt,  G.  M.,  The  preservative  treatment  of  farm  timbers.  U.  S. 
Dept.  Agr.  Farms'.  Bui.  7U-  1916.  397.  Wier,  J.  R.,  Larch 
mistletoe:  some  economic  considerations  of  its  injurious  elTects. 
U.  S.  Dept.  Agr.  Bui.  S/7.  1916.  398.  Shear,  C.  L.,  Grape  anthrac- 
nose  in  America.  Int.  Cong.  Vit.  San  Francisco.  1915.  399. 
Hartley,  C,  Merrill,  T.  C,  and  Rhoades,  A.  S.,  Seedling  diseases  of 


484  Bibliography 

conifers.  Jour.  Agr.  Res.  15:  521.  1918.  400.  Reddick,  D.,  and 
Gladwin,  F.  E.,  Powdery  mildew  of  grapes  and  its  control  in  the 
United  States.  Int.  Cong.  Vit.  San  Francisco.  1915.  401.  Collins, 
J.  F.,  Practical  tree  surgery.  U.  S.  Dept.  Agr.  Yearbook  1913:  163. 
1914.  402.  Stone,  G.  E.,  Shade  trees.  Mass.  Agr.  Exp.  Sta.  Bui. 
170.  1916.  403.  Peets,  E.,  Practical  tree  repair.  McBride  & 
Co.  1916.  404.  Schrenk,  H.  v.,  A  disease  of  the  white  ash  caused 
by  Polyporus  fraxinophilus.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  32. 
1903.  405.  Schrenk,  H.  v..  The  hardy  catalpa.  U.  S.  Dept.  Agr. 
Bur.  For.  Bui.  37.  1902.  406.  Kern,  F.  D.,  A  biologic  and  tax- 
onomic  study  of  the  genus  Gymnosporangium.  Bui.  N.  Y.  Bot. 
Card.  7:  391.  1911.  407.  Schrenk,  H.  v..  White  rot  of  the  red 
cedar.  U.  S.  Dept.  Agr.  Div.  Veg.  Phys.  &  Path.  Bui.  21.  1900. 
408.  Shear,  C.  L.,  et  al.,  Endothia  parasitica  and  related  species. 
U.  S.  Dept.  Agr.  Bui.  380.  1917.  409.  Anderson,  J.  P.,  and  Ran- 
kin, W.  H.,  Endothia  canker  of  chestnut.  N.  Y.  (Cornell)  Agr. 
Exp.  Sta.  Bui.  347.  1914.  410.  Barss,  H.  P.,  A  new  filbert  disease 
in  Oregon.  Bien.  Crop  Pest  and  Hort.  Rept.  ^.- 213.  1915.  411. 
Weir,  J.  R.,  and  Hubert,  E.  E.,  A  study  of  heart-rot  in  western 
hemlock.  IT.  S.  Dept.  Agr.  Bui.  722.  1918.  412.  Stewart,  V.  B., 
The  leaf  blotch  of  horse  chestnut.  N.  Y.  (Cornell)  Agr.  Exp.  Sta. 
Bui.  371.  1916.  413.  Humphry,  J.  E.,  A  hazel  fungus.  Mass. 
(Amherst)  Agr.  Exp.  Sta.  Rept.  10:  242.  414.  Schrenk,  H.  v., 
A  disease  of  the  black  locust.  Mo.  Bot.  Gard.  Rept.  12:  21.  1901. 
415.  Rand,  F.  V.,  Some  diseases  of  pecans.  Jour.  Agr.  Res.  4' 
303.  1914.  416.  Matz,  J.,  Diseases  and  insect  pests  of  the  pecan. 
Fla.  Agr.  Exp.  Sta.  Bui.  I47.  1918.  417.  Orton,  W.  A.,  and 
Rand,  F.  V.,  Pecan  rosette.  Jour.  Agr.  Res.  3:  149.  1914.  418. 
McMurran,  S.  M.,  Pecan  rosette  in  relation  to  soil  deficiencies. 
U.  S.  Dept.  Agr.  Bui.  736.  1919.  419.  Spaulding,  P.,  The  white- 
pine  blister  rust.  U.  S.  Dept.  Agr.  Farms'.  Bui.  742.  1916.  420. 
Spaulding,  P.,  The  blister  rust  of  white  pine.  IT.  S.  Dept.  Agr., 
B.  P.  I.  Bui.  206.  1911.  421.  Schrenk,  H.  v.,  The  bluing  and  the 
red-rot  of  the  western  yellow  pine  with  especial  reference  to  the 
black  hills  forest  reserve.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  36.  1903. 
422.  Hedgcock,  G.  G.,  and  Hunt,  N.  R.,  Dothichiza  populea  in  the 
United -States.    Myc.  8:  300.    1916.    423.  McMurran,  S.  M.,  Wal- 


Bibliography  485 

nut  blight  in  the  eastern  United  States.  IT.  S.  Dept.  Agr.  Farms'. 
Bui.  611.  1917.  424.  Smith,  R.  E.,  Walnut  culture  in  California. 
Walnut  blight.  Cal.  Agr.  Exp.  Sta.  Bui.  ^Si.  1912.  425.  Fawcett, 
H.  S.,  Melaxuma  of  the  walnut.  Cal.  Agr.  Exp.  Sta.  Bui.  261. 
1915.  426.  Smith,  R.  E.,  Growing  China  asters.  Mass.  Agr.  Exp. 
Sta.  Bui.  79.  1902.  427.  Townsend,  C.  0.,  A  soft-rot  of  the  calla 
Hly.  U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  60.  1904.  428.  Arthur,  J.  C, 
Bot.  Gaz.  321.  1891.  429.  Stewart,  F.  C,  Combating  carnation 
rust.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Bui.  100.  1896.  430.  Stevens, 
F.  L.,  and  Hall,  J.  G.,  Carnation  alternariose.  Bot.  Gaz.  47-'  409. 
1909.  431.  Woods,  A.  F.,  Bacterial  spot,  a  new  disease  of  carna- 
tions. Sc.  n.  s.  18:  537.  1903.  432.  Stewart,  F.  C,  The  stem-rot 
diseases  of  the  carnation.  Bot.  Gaz.  27:  129.  1899.  433.  Stewart, 
F.  C,  Notes  on  various  plant  diseases.  N.  Y.  (Geneva)  Agr.  Exp. 
Sta.  Bui.  164.  1899.  434.  Stewart,  F.  C,  and  Hodgkiss,  H.  E., 
The  Sporotrichum  bud-rot  of  carnations  and  the  silver  top  of  June 
grass.  N.  Y.  (Geneva)  Agr.  Exp.  Sta.  Tech.  Bui.  7.  1908.  435. 
Beach,  S.  A.,  Leaf  spot  of  chrysanthemums.  N.  Y.  (Geneva)  Agr. 
Exp.  Sta.Rept. //.•557.  1893.  436.  Arthur,  J.  C,  Chrysanthemum 
rust.  Ind.  Agr.  Exp.  Sta.  Bui.  85:  150.  1900.  437.  Stevens,  F. 
L.,  The  chrysanthemum  ray-blight.  Bot.  Gaz.  44:  241.  1907. 
438.  Harter,  L.  L.,  Storage-rots  of  economic  aroids.  Jour.  Agr. 
Res.  6'.-  549.  1916.  439.  Arthur,  J.  C,  Disease  of  clematis.  N.  Y. 
(Geneva)  Agr.  Exp.  Sta.  Rept.  3:  383.  1884.  440.  Stewart,  F.  C, 
Notes  on  New  York  plant  diseases.  N.  Y.  (Geneva)  Agr.  Exp. 
Sta.  Bui.  328.  1910.  441.  Gloyer,  W.  0.,  Ascochyta  clematidina, 
the  cause  of  stem-rot  and  leaf-spot  of  clematis.  Jour.  Agr.  Res.  4-' 
331.  1915.  442.  Massey,  L.  M.,  The  hard  rot  disease  of  gladiolus. 
N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  380.  1916.  443.  Ward,  H.  M., 
A  lily  disease.  Ann.  Bot.  2:  319.  '  1888.  444.  Woods,  A.  F.,  The 
Bermuda  lily  disease.  U.  S.  Dept.  Agr.  Div.  Veg.  Phys.  &  Path. 
Bui.  14.  1897.  445.  Smith,  C.  O.,  A  bacterial  disease  of  oleander. 
Bot.  Gaz.  4^;  301.  1906.  446.  Smith,  R.  E.,  A  new  Colletotrichum 
disease  of  the  pansy.  Bot.  Gaz.  27:  203.  1899.  447.  Wolf,  F.  A., 
A  Fusarium  disease  of  the  pansy.  Myc.  2:  19.  1910.  448.  Pat- 
terson, Mrs.  Flora,  and  Charles,  Vera  K.,  Disease  of  peonies  caused 
by  Botrytis.     U.  S.  Dept.  Agr.,  B.  P.  I.  Bui.  171.     1910.     449. 


486  Bibliography 

Wolf,  F.  A.,  Black-spot  of  roses.  Ala.  Agr.  Exp.  Sta.  Bui.  17:2.  1913. 
450.  Anderson,  P.  J.,  Rose  canker  and  its  control.  Mass.  Agr. 
Exp.  Sta.  Bui.  183.  1918.  451.  Jenkins,  A.  E.,  Brown  canker  of 
roses  caused  bj^  Diaporthe  umbrina.    Jour.  Agr.  Res.  15:  593.    1918. 

452.  Stewart,  F.  C,  An  anthracnose  and  a  stem-rot  of  the  cultivated 
snapdragon.     N.  Y.   (Geneva)  Agr.  Exp.  Sta.  Bui.  179.     1900. 

453.  Peltier,  L.  R.,  Snapdragon  rust.  111.  Agr.  Exp.  Sta.  Bui.  2^21. 
1919.  454.  Taubenhaus,  J.  J.,  The  diseases  of  the  sweet  pea.  Del. 
Agr.  Exp.  Sta.  Bui.  106.  1914.  455.  Lawrence,  W.  H.,  Plant 
diseases  induced  by  Sclerotinia  perplexa,  nov.  sp.  Wash.  Agr.  Exp. 
Sta.  Bui.  107.  1912.  456.  Dorsett,  P.  H.,  vSpot  disease  of  the  violet. 
U.  S.  Dept.  Agr.,  Div.  Veg.  Phyr3.  &  Path.  Bui.  S3.  1900.  457. 
Coleman,  D.  A.,  and  Regan,  S.  A.,  Nematode  galls  as  a  factor  in  the 
marketing  and  milling  of  wheat.  U.  S.  Dept.  Agr.  Bui.  734-  1918. 
458.  Whetzel,  H.  H.,  Some  diseases  of  beans.  N.  Y.  (Cornell) 
Agr.  Exp.  Sta.  Bui.  ^39.  1906.  459.  Smith,  R.  E.,  Tomato  diseases 
in  California.  Cal.  Agr.  Exp.  Sta.  Bui.  175.  1906.  460.  Atkinson, 
G.  F.,  (Edema  of  the  tomato.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui. 
53.  1893.  461.  Clinton,  G.  P.,  The  smuts  of  Illinois  Agricultural 
plants.  111.  Agr.  Exp.  Sta.  Bui.  57.  1900.  462.  Lind,  J.,  The  bar- 
berry bush  and  its  law.  Denmark  Ms.  translation  issued  by  the 
U.  S.  Dept.  of  Agr.  463.  Wilcox,  E.  M.,  A  leaf-curl  disease  of 
oaks.  Ala.  Agr.  Exp.  Sta.  Bui.  1£6.  1903.  464.  Fairchild,  D.  G., 
A  mignonette  disease.  U.  S.  Dept.  Agr.  Rept.  89:  429.  1889.'  465. 
Gregory,  C.  T.,  Studies  on  Plasmopara  viticola  (downy  mildew  of 
grapes).  Int.  Cong.  Vit.  San  Francisco.  1915.  466.  Massey,  L. 
M.,  The  diseases  of  roses.  Trans.  Mass.  Hort.  Soc.  1918.  467. 
Beach,  W.  S.,  The  Fusarium  wilt  of  China  asters.  Mich.  Acad.  Sc. 
Rept.  20.  1918.  468.  Kunkel,  L.  O.,  Wart  of  potatoes:  a  disease 
new  to  the  United  States.  U.  S.  Dept.  Agr.,  B.  P.  I.  Cir.  6.  C.  T. 
&  F.  C.  D.  1919.  469.  Johnson,  J.,  and  Milton,  R.  H.,  Strains 
of  white  Burley  tobacco  resistant  to  root-rot.  U.  S.  Dept.  Agr. 
Bui.  765.  1919.  470.  Coons,  G.  H.,  An  undescribed  bark  canker 
of  apple  and  the  associated  organisms.  Mich.  Acad.  Sc.  Rept.  17. 
1915.  471.  Faulwetter,  R.  C,  The  angular  leaf  spot  of  cotton. 
S.  C.  Agr.  Exp.  Sta.  Bui.  198.  1919.  472.  Colby,  A.  S.,  Sooty 
blotch  of  apples.    To  be  published  in  Trans.  111.  Acad.  Sc.    1919. 


Bibliography  487 

473.  Brooks,  C,  Effect  of  temperature,  aeration,  and  humidity  on 
Jonatiian-spot  and  scald  of  apples  in  storage.  Jour.  Agr.  Res.  2: 
287.  1917.  474.  Brooks,  C,  and  Cooley,  J.  S.,  Apple-scald.  Jour. 
Agr.  Res.  M.- 195.  1919.  475.  Fromme,  F.  D.,  and  Wingard,  S.  A., 
Bean  rust.  Va.  Agr.  Exp.  Sta.  Bui.  220.  1918.  476.  Carsner,  E., 
Angular  leaf-spot  of  cucumber.  Jour.  Agr.  Res.  i.5;  201.  1918.  477. 
MacMillan,  H.  G.,  Fusarium-blight  of  potatoes  under  irrigation. 
Jour.  Agr.  Res.  16:  279.  1919.  478.  Harter,  L.  L.,  Weimer,  J.  L., 
and  Adams,  J.  M.  R.,  Sweet  potato  storage  rots.  Jour.  Agr.  Res. 
15:  337.  1918.  479.  Fromme,  F.  D.,  Angular  leaf-spot  of  tobacco, 
an  undescribed  bacterial  disease.  Jour.  Agr.  Res.  16:  219.  1919. 
480.  Stevens,  F.  L.,  An  apple  canker  due  to  Cytospora.  111.  Agr. 
Exp.  Sta.  Bui.  217.  1919.  481.  Stevens,  F.  L.,  and  True,  E.  Y., 
Black  spot  of  onion  sets.  111.  Agr.  Exp.  Sta.  Bui.  220.  1919.  482. 
Byars,  L.  P.,  The  eelworm  disease  of  wheat  and  its  control.  U.  S. 
Dept.  Agr.  Farms'.  Bui.  lOU.  1919.  483.  Darnell-Smith,  G.  P., 
and  McKinnon,  E.,  Diseases  of  wheat.  N.  S.  Wales  Dept.  Agr. 
Farms'.  Bui.  102.  1915.  484.  Swingle,  D.  B.,  and  Morris,  H.  E., 
Plum  pocket  and  leaf  gall  of  American  plums.  Mont.  Agr.  Exp.  Sta. 
Bui.  123.  1918.  485.  Stevens,  F.  L.,  Foot-rot  disease  of  wheat- 
historical  and  bibliographic.  111.  Nat.  Hist.  Surv.  Bui.  13,  Art.  9. 
1919.  486.  Johnson,  E.  C.,  Timothy  rust  in  the  United  States. 
U.  S.  Dept.  Agr.  B.  P.  I.  Bui.  22^.  1911.  487.  Jones,  F.  R.,  The 
leaf  spot  diseases  of  alfalfa  and  red  clover  caused  by  the  fungi 
pseudopeziza  medicaginis  and  Pseudopeziza  trifolii,  respectively. 
U.  S.  Dept.  Agr.  Bui.  759.  1919.  488.  Stevens,  F.  L.,  Progress  in 
control  of  plant  diseases-.  Pop.  Sc.  Mo.  May.  1911.  489.  Hasse, 
Clara  H.,  Pseudomonas  citri,  the  cause  of  citrus-canker.  (A  pre- 
liminary report.)  Jour.  Agr.  Res.  J^:  97.  1915.  490.  Tanaka, 
Tyzaburo,  A  brief  history  of  the  discovery  of  citrus-canker  in 
Japan  and  experiments  in  its  control.  Quart.  Bui.  State  Plant  Bd. 
Fla.  3;  1.  1918.  491.  Berger,  E.  W.,  Citrus-canker  in  the  Gulf 
coast  country,  with  notes  on  the  extent  of  citrus  culture  in  the 
localities  visited.  Proc.  27th  Ann.  Meeting,  Fla.  State  Hort. 
Soc.  120.  1914.  492.  Stirling,  Frank,  Eradication  of  citrus  canker. 
Fla.  Agr.  Exp.  Sta.  Bui.  12J^:  44.  1914.  493.  Stakman,  E.  C, 
Piemeisel,  F.  J.,  Biologic  forms  of  Puccinia  graminis  on  cereals  and 


488  Bibliography 

grasses.  Jour.  Agr.  Res.  10:  480.  1917.  494.  Duke  of  Bedford  and 
Pickering,  S.  U.,  Potato  spraying.  Woburn  Exp.  Fruit  Farm,  Rept. 
14:1.  1914.  495.  Pickering,  S.  U.,  Copper  fungicides.  Jour.  Agr. 
Sc.  4:  273.  1912.  496.  Metcalf,  H.,  and  Collins,  J.  F.,  The  present 
status  of  the  chestnut  bark  disease.  U.  S.  Dept.  Agr.  B.  P.  I.  Bui. 
141-  1909.  497.  Hawkins,  L.  A.,  Some  factors  influencing  the 
efficiency  of  Bordeaux  mixture.  U.  S.  Dept.  Agr.  B.  P.  I.  Bui.  265. 
1912.  498.  Ruth,  W.  A.,  Spraying  experiments  in  1912  at  Flora, 
Clay  county.  111.  Agr.  Exp.  Sta.  Bui.  185:  107.  1916.  499.  Van 
Slyke,  L.  L.,  Bosworth,  A.  W.,  and  Hedges,  C.  C,  Chemical  investi- 
gation of  best  conditions  for  making  lime-sulphur  wash.  New  York 
(Geneva)  Agr.  Exp.  Sta.  Bui.  329.  1910.  500.  Blodgett,  F.  M., 
Experiments  in  the  dusting  and  spraying  of  apples.  N.  Y.  (Cornell) 
Agr.  Exp.  Sta.  Bui.  340.  1914.  601.  Reddick,  Donald  and  Crosby, 
C.  R.,  Further  experiments  in  the  dusting  and  spraying  of  apples. 
N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  354-  1915.  502.  Reddick, 
Donald  and  Crosby,  C.  R.,  Dusting  and  spraying  experiments,  with 
apples.  N.  Y.  (Cornell)  Agr.  Exp.  Sta.  Bui.  369.  1916.  503. 
Stewart,  V.  B.,  Dusting  and  spraying  nursery  stock.  N.  Y.  (Cor- 
nell) Agr.  Exp.  Sta.  Bui.  385.  1917.  504.  Hoffer,  G.  N.,  and  John- 
son, A.  G.,  Atanasoff,  D.,  Corn  root  rot  and  wheat  scab.  Jour.  Agr. 
Res.  ^4;  611.  1918.  505.  Brock,  W.  S.,  Results  of  spraying  experi- 
ments at  Neoga  Station,  Cumberland  County,  1916.  Trans.  III. 
Hort.  Soc.  50:  260.  1916.  506.  Hoffer,  G.  N.,  and  Holbert,  J.  R., 
Selection  of  disease  free  seed  corn.  Ind.  Agr.  Exp.  Sta.  Bui.  224- 
1918.  507.  Wallace,  Errett,  and  Evans,  L.  H.,  Commercial  Bor- 
deaux Mixtures.  U.  S.  Dept.  Agr.  Fanns'  Bui.  994.  1913.  508. 
Crane,  H.  L.,  A  study  of  the  factors  governing  the  efficiency  of  dis- 
tribution and  rate  of  discharge  of  spraj'^  nozzles.  W.  Va.  Agr.  Exp. 
Sta.  Bui.  169.  1919.  509.  Childs,  Leroy,  New  facts  regarding  the 
period  of  ascospore  discharge  of  the  apple  scab  fungus.  Oregon  Agr. 
Exp.  Sta.  Bui.  143.  1917.  510.  Blair,  W.  S.,  Ann.  Rept.  Fruit 
Growers'  Assoc.  Nova  Scotia,  132-159.  1917.  511.  Morse,  W.  J., 
Apple  spraying  experiments  in  1916  and  1917.  Maine  Agr.  Exp.  Sta. 
Bui.  271.  1918.  512.  Fromme,  F.  D.,  and  Ralston,  G.  S.,  Dusting 
Experiments  in  peach  and  apple  orchards.  Va.  Agr.  Exp.  Sta.  Bui. 
223.  1919.  513.  Hedrick,U.  P.,  Bordeaux  injury.  N.  Y.  (Geneva) 
Agr.  Exp.  Sta.  Bui.  287:  142.    1907.    514.  Wallace,  Errett,  Spray 


Bibliography  489 

injury  induced  by  lime-sulfur  preparations.  N.  Y.  (Cornell)  Agr. 
Exp.  Sta.  Bui.  288:  123-12.5.  1910.  515.  Talbert,  T.  J.,  Combined 
dormant  and  first  summer  spray  in  apple  orchards  infested  by  San 
Jose  scale.  Mo.  Agr.  Exp.  Sta.  Bui.  ^e^.  1919.  516.  Pollock,  J.  B., 
The  longevity  in  the  soil  of  the  Sclerotinia  causing  the  brown-rot 
of  stone  fruits.  Mich.  Acad.  Sci.  Rept.  20:  279.  1918.  517.  Bain, 
S.  M.,  The  action  of  copper  on  leaves.  Tenn.  Agr.  Exp.  Sta.  Bui. 
Vol.  15,  No.  2:  44.  1902.  518.  Crandall,  C.  S.,  Bordeaux  mixture. 
111.  Agr.  Exp.  Sta.  Bui.  1S5:  233.  1909.  519.  Selby,  A.  D.,  A  brief 
handbook  of  the  diseases  of  cultivated  plants  in  Ohio.  Ohio  Agr. 
Exp.  Sta.  Bui.  214.  1910.  520.  Pammel,  L.  H.,  King,  C.  M.,  Seal, 
J.  L.,  Studies  on  a  Fusarium  disease  of  corn  and  sorghum,  la.  Agr. 
Exp.  Sta.  Res.  Bui.  33.  1916.  521.  Gunderson,  A.  J.,  Field  expe- 
rience in  spraying  apple  orchards  for  the  control  of  apple  blotch. 
111.  Agr.  Exp.  Sta.  Bui.  222.  1919.  522.  Schoene,  W.  J.,  and 
Reppert,  R.  R.,  Growth  of  apple  trees  injured  by  crown  gall  and 
woolly  aphis.    Quart.  Bui.  Va.  State  Crop.  Pest.  Comm.,  /.  No.  2. 

1919.  523.  Ball,  E.  D.,  The  potato  leafhopper  and  its  relation  to 
the  hopperburn.  Journ.  Econ.  Ent.  Ames,  Iowa,  12:  149.  1919. 
524.  Guba,  E.  F.,  and  Anderson,  P.  J.,  Phyllosticta  leaf  spot  and 
damping  off  of  snapdragons.  Phytop.  9:  315.  1919.  525.  Hum- 
phrey, H.  B.,  and  Johnson,  A.  G.,  Take  all  and  flag  smut,  two  wheat 
diseases  new  to  the  U.  S.  U.  S.  Dept.  Agr.  Farms'.  Bui.  1063.  1919. 
526,  Humphrey,  H.  B.,  Cereal  diseases  and  the  national  food  sup- 
ply. U.  S.  Dept.  Agric.  Yearbook  1917:  481.  1918.  527.  Tisdale, 
W.  B.,  Iris  leaf  spot  caused  by  Didjanellina  iridis.    Phytop.  10:  147. 

1920.  528.  Hoffer,  G.  N.,  Disease  free  sweet  corn  seed.  Ind.  Agr. 
Exp.  Sta.  Bui.  233:  1920.  529.  Peltier,  G.  L.,  Carnation  stem  rofand 
its  control.  111.  Agr.  Exp.  Sta.  Bui.  223:  1919.  530.  Long,  W.  H., 
An  undescribed  canker  of  poplars  and  willows  caused  by  Cytospora 
chrysosperma.  Jour.  Agr.  Res.  13:  331.  1918.  531  Bisby,  G.  R., 
Studies  on  Fusarium  diseases  of  potatoes  and  truck  crops  in  Min- 
nesota. Minn.  Agr.  Exp.  Sta.  Bui.  181.  1919.  532.  Tisdale,  W. 
H.,  Bacterial  blight  of  soy  bean.  N.  C.  Agr.  Exp.  Sta.  Rept.  1918. 
59.  533.  Coerper,  Florence  M.,  Bacterial  blight  of  soybean.  Jour. 
Agr.  Res.  18:  179.  1919.  534.  Wolf,  F.  A.,  Bacterial  blight  of 
soybean.  Phytop.  ^0.- 1920.  535.  Wolf,  F.  A.,  and  Cromwell,  R.  O., 
Clover  stem  rot.    N.  C.  Agr.  Exp.  Sta.  Tech.  Bui.  16.    1919.    536. 


490  Bibliography 

Fisher,  D.  F.,  and  Newcoml:),  E.  J.,  Controlling  important  fungous 
and  insect  enemies  of  the  pear  in  the  humid  sections  of  the  Pacific 
northwest.  Farms'.  Bui.  1056.  1919.  537.  Fromme,  F.  D.,  The 
Nematode  disease  of  wheat  in  Virginia.  Va.  Agr.  Exp.  Sta.  Bui. 
222.  1919.  538.  Stakman,  E.  C,  and  Levine,  M.  N.,  Rye  smut. 
Minn.  Agr.  E.xp.  Sta.  Bui.  160.  1916.  539.  Byars,  L.  P.,  and  Gil- 
bert, W.  W.,  Soil  disinfection  with  hot  water  to  control  the  root- 
knot  nematode  and  parasitic  soil  fungi.  U.  S.  Dept.  Agr.  Bui.  818. 
1920.  540.  Rand,  Frederick  B.,  and  Ella  M.  A.  Enlows,  Bacterial 
wilt  of  cucurbits.  U.  S.  Dept.  Agr.  Bui.  8'£8.  1920.  541.  Schultz, 
E.  S.,  Folsom,  D.,  Hildebrandt,  F.M.,  and  Hawkins,  L.  A.,  Investi- 
gations of  the  mosaic  disease  of  the  Irish  potato.  Jour.  Agr.  Res. 
17:  247.  1919.  542.  Meier,  F.  C,  Control  of  watermelon  anthrac- 
nose  by  spraying.  U.  S.  Dept.  Agr.  Circ.  90.  1920.  543.  McMur- 
ran,  S.  M.,  The  anthracnose  of  the  mango  in  Florida.  U.  S.  Dept. 
Agr.  Bui.  52.  1914.  544.  Stevens,  N.  E.,  and  Morse,  F.  W.,  The 
effect  of  the  endrot  fungus  on  cranberries.  Amer.  Jour.  Bot.  6:  235. 
1919.  545.  Higgins,  B.  B.,  A  Collectotrichum  leafspot  of  turnips. 
Jour.  Agr.  Res.  10:  157.  1917.  546.  Brandes,  E.  W.,  Banana  wilt. 
Phytop.  9:  339.  1919.  547.  Quanjer,  H.  M.,  The  mosaic  disease 
of  the  solanacese,  its  relation  to  the  phloem-necrosis,  and  its  effect 
upon  potato  culture.  Phytop.  10:  35.  1920.  548.  Botjes,  J.  0., 
Raising  phloem-necrosis  and  mosaic  free  potatoes,  and  a  source  of 
infection  whose  nature  has  not  yet  been  elucidated.  Phytop.  10: 
48.  1920.  549.  Orton,  C.  R.,  and  Kern,  F.  D.,  The  potato  wart 
disease.  Penn.  Agr.  Exp.  Sta.  Bui.  156.  1919.  550.  Walker,  J.  C, 
Onion  diseases  and  their  control,  U.  S.  Dept.  Agr.  Farms'.  Bui. 
1060.  1919.  551.  Stakman,  E.  C,  The  black  stem  rust  and  the 
barberry.  U.  S.  Dept.  Agr.  Yearbook,  1918:  75.  1919.  552. 
Rosen,  H.  R.,  A  Bacterial  root-rot  of  field  corn.  Ark.  Agr.  Exp. 
Sta.  Bui.  162.  1919.  553.  Taubenhaus,  J.  J.,  Field  diseases  of  the 
sweet  potato  in  Texas.  Texas  Agr.  Exp.  Sta.  Bui.  249.  1919.  554. 
Stevens,  F.  L.,  Foot-rot  of  wheat.  Sc.  N.  S.  5^- 517.  1920.  555. 
Greene,  Laurenz  and  Melhus,  I.  E.,  The  effect  of  crown  gall  upon 
a  young  apple  orchard.  Iowa  Agr.  Exp.  Sta.  Res.  Bui.  50.  1919. 
556.  Miles,  L.  E.,  Elm  leaf  diseases.  To  be  published  in  the 
Botanical  Gazette. 


INDEX 


Abutilon,  407. 

Acalypha,  407. 

Acanthorhynchus   vaccinii,    111. 

Acanthostigma,   379. 

Achillea,   407. 

Acremonium,    191. 

Actinomyces  scabies,   163,  220. 

Actinonema,    430. 

Adonis,   407. 

iEcidium,  119,  .390,  411,  423. 

gossypii,  350. 
Agave,    408. 
Ageratum,  407. 
Agropyron,  277,  278,  ,340. 
Agrostis,   277,  278,   340. 
Aira,  278. 
Albugo,   173,  408. 

bliti,   164. 

Candida,    172,    196,   427. 

ipomoeae-panduranse,  250,  427. 

tragopogonis,   241. 
Alder,    361,    367,     369,     371,    379, 

381. 
Alfalfa,  22,  23,  24,  88,  163,  321. 
Algal  leaf-spot,   144,   147. 
Allseed,    163. 
Almond,  25,  74,  87. 
Alopecurus,  277,  278. 
Alternaria,    57,    69,    195,    217,    328, 
352,    415,    427. 

brassicae,  169. 

var.  nigrescens,  183. 

citri,  141. 

dianthi,  415. 

panax,    193. 

solani,  226,  264. 

violse,   436. 
Alyssum,  407. 
Amarantus,  407,  408. 
Amerosporium  oeconomicum,   335. 
Ammoniacal        copper       carbonate, 
447. 


Ampelopsis,  439. 

Andromeda,   409. 

Anemone,  407,  409. 

Angular    leaf-spot,    114,    185,    257, 

337,  349,  424. 
Anthostomella,   145. 
Anthoxanthum,    277,    278. 
Anthracnose,    102,    112,    115,    119, 
128,    135,    143,    147,    151.    152, 
173,    180,    192,    194,    199,    217, 
241,    242,    264,    280,    300,    307, 
309,    317,    324,    328,    330,    331, 
339,    340,    342,    345,    383,    388, 
392,    .395,    408,    409,    412,    421, 
424,    428,    420,    430,    433,    434, 
435,   437. 
Antirrhinum,   407. 
Aposphaeria,   134. 
Apple,    23,    31.    87.   361,   367,    368. 

369,   372. 
Apricot,  74,  87.  90. 
Aquilegia,  407. 
Aralia,  408. 

Arbor-vit«,  367,  369,  371.  380. 
Arbutus,   88. 
Armillaria,   117,  367. 
mellea,   53,   370. 
root-rot,  79,  96,  101. 
Arrenantheruni,  277. 
Arsenical  injury,  240. 
Artichoke,  435. 

Ascochyta,   1.34,  210,  369,  379. 
abelmoschi,  201. 
armoraciae,  195. 
chrysanthemi,  419. 
clematidina,   420. 
leaf -spot,  327. 
medicaginis,   327. 
primulse,  429. 
Ash,    23,    364,    367,   368,   369,    379, 

380,   .381. 
Aisparagus,  10,  25,  149,  407. 


491 


492 


Index 


Aspen,  359,  367. 
Aspidistra,  409. 
Aster,  22. 

china,    409. 
Asterina,  379. 
Auouba,    407. 
Avena,  277,  278. 
Avocado,    135. 
Azalea,  113,  411. 

Bacillus,  427. 

amylovorus,    41,   62,   70,   74,   79. 
101. 

carotovorus,    172,    173,    178,   208, 
412,   420. 

coli,    144. 

lathyri,  435. 

melonis,    188. 

phytophthorus,    231. 

sorghi,  307. 

tracheiphilus,  182. 
Bacteria,    217,    299,   304,   342,    369, 

389,   426. 
Bacterial  blight,  213,  337. 

leaf-spot,  164,  422. 

rot,  199. 

spotting,  200,  416. 

wilt,   260. 
Bacterium    michiganense,    260. 

mori,   393. 

rathayi,  339. 

teutlium,  164. 
Balm,  411. 
Balsam,    367. 
Bamboo,  411. 
Banana,   135. 
Barberry,  312,  411. 
Bark  canker,  56,  69. 


Barley,  163,  280. 

Barnyard-grass,  338. 

Barrel    pump,    454. 

Bartonia,  407. 

Basswood,    372. 

Bean,  22,  23,  25,  152,  163. 

Beckmannia,    277. 

Bed-rot,  257. 

Beech,  359,  361,  364,  365,  367,  369, 

380    381 
Beet,  22,  23,  25,  27,  87,  159,  163. 
Begonia,  24,  407,  408,  412. 


Bellflower,  23. 

Berberis,   407. 

Bermuda  lily  disease,  426. 

Birch,  359,  361,  364,  365,  367,  368, 
369,  371,  379,  380,  381,  382. 

Bitter-pit,  54. 

Bitter-rot,  31,  69,  72,  132. 

Blackberry,   87,    102. 

Black-chaff,  319. 

Black-heart,  148,  235. 

Black-knot,  75,  97. 

Blackleg,    169,   231. 

Black-mold,  57,  69,  169,  196,  210, 
213,  216,  243,  328,  .331,  427. 

Black-root,  163,  173. 

Black-rot,  42,  47,  72,  120,  141,  165, 
194,  247,  260. 

Black-rot  canker,  69. 

Black-rust,   350. 

Black-scurf,  225. 

Black-smut,   146,  .302. 

Black-spot,  70,  74,  79,  90,  101,  205, 
217. 
canker,  430. 

Black-stem-rust,  282,  298,  305,  310, 
339,  340. 

Black-walnut,  359. 

Blast,   110,  339,  380. 

Bletia,   412. 

Blight,  62,  70,  74,  79,  101,  144,  155, 
165,  193,  195,  199,  203,  242, 
251,  260,  282,  294,  299,  307, 
324, 389,  393,  394,  403,  404,  421, 
422,  425,  427.  (See  also  early- 
blight,  southern-blight,  late- 
blight,  blister-blight,  blossom- 
blight,  brown- blight,  bacter- 
ial-blight, body-blight,  pod- 
blight,  stem-blight,  coryneum- 
bhght,  leaf-blight,  cane-blight.) 

Blister-cankei,  44. 

Blister-rust,    119,   395. 

Blossom-blight,   41. 

Blossom-drop,    265. 

Blossom-end  rot,  263. 

Blossom  rot,   191. 

Blotch,  37. 

Blueberry,    110. 

Bluegrass,  280,  338. 

Blue-mold,  51,  108,  132,  141,  193, 
250. 


Index 


493 


Blue-stem,    110. 
Bluing,  397. 
Body-blight,  41. 
Boll-rot,  .346. 
Bordeaux-injury,  450. 
Bordeaux  mixture,  6,  440. 
Botryosphaeria,  346. 

berengeriana,   395. 

marconii,  353. 

ribis,  113. 
Botrytis,  10,  20,  174,  369,  416,  421, 
422,  426,  427,  428,  430,  436. 

ailii,   206. 

blight,    195. 

cinerea,    198. 

fascicularis,   192. 

rot,  134. 
Box-elder,  369. 
Breeding  for  resistance,  7. 
Bremia  lactucae,   198. 
Broccoli,    165. 
Bromus,  277,  278. 
Bronzing,  433. 
Broom  corn,  283. 
Broom  rape,  .331. 
Brown-canker,  432. 
Brown-checked  wood-rot,  361. 
Brown  leaf-rust,  305. 
Brown  leaf-spot,  395. 
Brown-rot,   55,   69,   73,   74,   75,   79, 

101,    135. 
Brown-spot,   292. 
Brunnissure,    131. 
Brussels-sprouts,  163,  165. 
Bucket   pumps,   452. 
Buckeye,  390. 
Buckeye-rot,  265. 
Buckwheat,  22,  165. 
Bud-rot,  144,  417. 
Bunt,  314. 

Burgundy  mixture,  448. 
Butternut,  .359,  361,  367,  380,  381, 
382. 

Cabbage,  22,  23,  26,  163,  165. 

Cacao,  135. 

Cacao-disease,    245. 

Calamagrostis,  277,  278. 

Calendula,    407. 

California  vine-disease,  131. 

Calla,  412. 


Callistephus,  407,  409. 
Calospora  vanillse,  148. 
Camelha,  408,  413. 
Campanula,  407,  408. 
Candytuft,  168. 
Cane-blight,  105,  113. 
Canker,  32,  35,  42,  69,  72,  135,  137, 
146,    251,    368,    385,    .390,    401, 
402,  405,  423,  432.      (See  also 
Pacific    coast    canker,     blister- 
canker,  black-rot  canker,  brown 
canker.) 
Canna,  413. 
Cantaloupe,    173. 
Caper,    173. 

Capnodium,  144,  408,  413. 
Carnation,  22,  87,  414. 
Carrot,  22,  23,  25,  173. 
Cassandra  calyculata,  113. 
Castor-bean,    174. 
Catalpa,    25,    368,    373,    379,    380, 

381,   382. 
Cauliflower,  23,  163,  165. 
Cedar,  69,  367,  383. 
Celery,  22,  25,  163,  174. 
Celosia,  407. 
Cenangium,   369. 
Centaurea,   407. 
Cephaleuros,    251. 

virescens,  144,  147. 
Cephalothecium,   395. 

roseum,  49. 
Ceratostomella  pilifera,  397. 
Cercospora,    201,    217,    348,    379, 
439,   524. 

althseina,   424. 

angulata,   114. 

apii,  176. 

armoraciae,   196. 

beticola,  159,  244. 

bolleana,   146. 

capsici,   217. 

circumscissa,  96. 

coffeicola,  145. 

concors,    234. 

cruenta,   159,  337. 

fusca,    395. 

leaf-spot,     132,    159,     191,     327, 
331. 

longipes,  245. 

medicaginis,  327. 

microsora,  391. 


494 


Index 


nicotianse,  257. 

person ata,  214. 

phlogina,  429. 

resedfie,  426. 

richardiaecola,   413. 

rosseicola,  433. 

shot-hole,  96. 
Cercosporella    albomaculans,     173. 

persica,   96. 
Cereal,  266. 

anthracnose,  266. 

msts,   275. 

smuts,   266. 

special  diseases,  280. 
Chama;cyparis,  368,  369. 
Charcoal-rot,    251. 
Chard,   159. 
Charrina,   132. 
Cherry,  22,  25,  75,  87,  90,   96,  97, 

361,  367,  369. 
Chestnut,    11,    87,     361,    3B7,    3(i8, 
369,    371,    373,    380,    381,    386, 
388. 
China-berry.  23,  369,  372. 
Chive,   201. 

Chlorosis,  148,  265,  295. 
Choanephora  cucurbitanini,    191. 
Chrysanthemum,  23,   88,   407,   408, 

418. 
Chrysophlyctis,   224. 
Cineraria,  24,  407,  420. 
Citrus   fruits,    135. 
Citrus  knot,   144. 
Cladosporium  carpophilum,  82,  99. 

citri,   142. 

cucumerinum,   187. 

fulvimi,   262. 

herbanmi,    140,   439. 

macrocarpum,    243. 

viticolum,    132. 
Ciaviceps  paspali,   340. 

purpurea,  304. 

rolfsii,  340. 
Cleistothecopsis  circinans,   205. 
Clematis,  24,  407,  420. 
Clethra  alnifoHa,   113. 
Clitocybe,  52,  372. 

root-rot,  96. 
Clover,  22,  24,  88,  163,  328. 
Club-root,  26,  168, 
Cluster-cup,  117,  119,  350,  409. 


Coccomyces,  75. 

prunophorse,   98. 
Cocoanut,    144. 
Coffee,  144. 
Coleosporium  ipomcEse,  251,  427. 

senecionis,  420. 

solidaginis,  401,  410. 
Coleus,  24,  407. 
Collard,  165. 

Colletotrichum,  20,  145,  148,  151, 
192,  205,  244,  251,  345,  352, 
379,  427,  428. 

agaves,  408. 

antirrhini,  434. 

bletise,  412. 

carica,    145. 

cereale,  280,  300,  307,  317. 

erumpens,  241. 

falcatum,  309. 

glceosporioides,  135,  143,  147. 

higginsianum,  173. 

lagenarium,  180. 

lindemuthianum,    152. 

malvarum,   424. 

nignmi,   217. 

omnivonmi,   409. 

phomoides,   264. 

primulse,  429. 

spinaceae,   242. 

trifolii,  324,  330. 

violse-tricoloris,  437. 
Collybia,  367. 
Colocasia,   420. 

Combined     fungicide     and     insecti- 
cide, 449. 
Common-scab,    220. 
Completoria  complens,  422. 
Compressed  air  sprayers,  453. 
Conifers,    355,    358,    361,    367,    368, 

369,  371,  376,  379,  380. 
Coniothyrium,   105,  395. 

fuckelii,  44. 
Conveyors,  457. 
Copper-blight,   251. 
Copper  sulfate,   448. 
Copper-sulfate  .treatment,  271. 
Coreopsis,  407. 

Core-rot,  57.  * 

Corn,  22,  88,  163,  283. 
Cornus,   408. 
Corrosive  sublimate,  449. 


Index 


495 


Corticium,  20,  135,  144,  146,  163, 
193,  194,  376,  402,  407.  410, 
435,  439. 

koleroga,  145. 

stevensii,  47. 

vagum,    21,    157,    162,    165,    198, 
213,  225,  257,  265,  349,  417. 
Coryneum  beijerinckii,    87. 
Coryneum-blight,  74,  87. 
Cosmos,   407,   421. 
Cotton,  22,  23,  24,  88. 
Cottonwood,  367,  369,  372,  380,  401. 
Cottony-rot,     137. 
Covered  smut,  282,  297. 
Cowpea,  23,  24,  26,  331. 
Crab-grass,  339. 
Cranberry,    110. 
Cress,   163. 
Cronartium,  369. 

cerebrum,   400. 

ribieola,  116,  395. 
Crown-gall,  51,  69,  73,  74,  79,  87, 
101,    104,    132,    164,    350,    405, 
408,  422,  433. 
Crown-rot,   144,  241. 
Crown-rust,  298,  339. 
Crown-wart,    325. 
Crucifers,  24,  165. 
Cryptosporella,   369. 

anomala,  389. 

viticola,  129. 
Cucumber,  22,  25,  26,  178. 
Cucurbit  spraying,  191. 
Cucurbits,  24,  178. 
Cuphea,    407. 
Cupressus,    369. 
Curing-house  disease,  259. 
Curl,  77,  84. 
Curly-dwarf,    233. 
Curly-top,    160. 
Currant,  22,  113,  367. 
Cuscuta,  325. 

epilinum,  352. 
Cutting-bench  disease,  407. 
Cuttings,  19. 
Cyanospora,    369. 
Cyclamen,  408,  421. 
Cycloconium   oleaginum,   147. 
Cylindrocladium  scoparium  432. 
Cylindrosporium,  75,  98,  379. 

chrysanthemi,  420. 


clematidis,    420. 

humuli,    195. 
Cypress,   367. 
Cystospora  batatae,  249. 
Cytospora,  78,  86,  369,  405,  423. 

chrysosperma,   401. 

Dactylis,  277,  278,  339. 

Dffidalea,   367. 

Dahlia,  24,  407,  408,  421. 

Daisy,  408,  422. 

Damage  caused   by   plant  diseases, 

10. 
Damping  off,  19,  24,  103,  173,  178, 
193,    194,    198,    213,    252,    258, 
265,   303,   328,   349,   352,   376, 
399,   427. 
Dandelion,    163. 
Daphne,  23. 
Dasyscypha,    369. 

resinaria,  390. 
Dead-arm,    129. 
Decay  in  live  trees,  354. 
Decay  of  dead  parts,  373. 
Deciduous  trees,  364,  365,  367,  368, 

371,   374. 
Dendrophoma,    353. 
Dewberrj',  88,  102. 
Dianthus,  407,  408. 
Diaporthe,    369. 

batatatis,  250. 

phaseolorum,    158. 

umbrina,  432. 
Dibotryon  morbosum,  75,  97. 
Didymellina  viridis,  425. 
Didvmosphseria,  379. 
Dieback,  74,  78,  86,  135,  144,  395, 
402,   404. 

canker,  57,  69. 
Diplocarpon  rosse,  430. 
Diplodia,    135,    144,    148,    187,  402, 
420. 

cacaoicola,  245. 

gossypina,    346. 

longispora,  394. 

macrospora,   287. 

tubericola,    250. 

zese,  287. 
Diplodina,    190. 
Diseases  due  to  impure  air,  26. 
Disease   prevention,   236. 


493 


Index 


Disinfection  of  seeds,  7. 

Doassansia  gossypii,  349. 

Dodder,  144,  325,  331,  352. 

Dogwood,  369,  381. 

Dothichiza,  369. 
populea,    401. 

Dothidea,   369. 

Dothidella,  394. 

Dothiorella  gregaria,  404. 

Double-blossom,    108. 

Downy-mildew,  125,  158,  164,  171, 
178,  196,  198,  203,  244,  263, 
295,  327,  338,  433,  437. 

Dracaena,  422. 

Dracocephalum,  408. 

Drop,  26,  27,  158,  164,  170,  174, 
193,  196,  258,  409,  426,  435. 

Drupes,  74,  368. 

Dry-rot,  230,  250,  287,  289,  374. 

Dusting  machines,  458. 

Dwarf  leaf-rust,  282. 

Early-blight,  176,  226,  264. 
Ear-rots,   286. 
Echinodontium,  367. 

tinctorum,    389. 
Eel-worms,    320,    412.       (See    also 

nematodes.) 
Egg  plant,  22,  23,  25,  26,  192. 
Einkorn,   310. 
Elder,    381. 
Elm,  23,  25,  359,  364,  367,  369,  379, 

380,  381,  388. 
Elymus,  277,  278. 
Emmer,    310. 
Endomyces,   57. 
Endothia,  369. 

parasitica,    386. 
End-rot,  112. 

Entomosporium,  68,  70,  379. 
Entyloma  ellisii,  242. 
Ergot,  282,  300,  304,  320,  339,  340. 
Erigeron,  408. 
Eriobotrya,  407. 
Erysimum,  407. 
Erysiphe,  173,  242,  338. 

cichoracearum,  420,  429,  436. 

communis,    421. 

graminis,  317. 

polygoni,  159,  165,  187,  213,  337. 
Eupatorium,    408. 


Euphorbia,  328,  407. 
European  canker,  55,  72,  401. 

rust,  116. 
Evonymus,  408. 
Exoascus   deformans,   84. 
Exobasidium,  110,  251,  409,  411. 

oxycocci,   112. 
Extension  rod,  458. 

Fabraea  maculata,  68,  70. 

mespili,  73. 
Falcata,  155. 
Favolus,  367. 
Ferns,  422. 
Festuca,   277,   278. 
Fiber-plant,  23,  343. 
Field  crops,  149. 
Field  sprayers,  454. 
Fig,   23,   25,    145. 
Filbert,  369,  389. 
Fir,  365,  367,  368,   369,  371,    373, 

380. 
Fire-blight,  41,  62,  74. 
Fistulina,  367. 
Flag-smut,   316. 
Flax,  23,  24,  26,  350. 
Flower-blight,  379. 
Flowering  almond,  408. 
Flowers  of  sulfur,  449. 
Flyspeck,  56,  69. 
Fomes,  367,  402. 

annosus,  53,  371. 

applanatus,    365. 

everhartii,    364. 

fomentarius,    364. 

fraxinophilus,  381. 

fulvus,  361. 

igniarius,  359. 

juniperinus,  383. 

pinicola,  365,  401. 

ribis,  117,  402. 

rimosus,  391. 
Foot-rot,  316. 
Forage  crops,  321. 
Formalin,   449. 
Formalin  dry  method,  270. 
Formalin  long-time  treatment,  271. 
Formalin  wet  method,  270. 
Foxtail,    163. 
Frost  injury,  54. 
Frosty-mildew,  96,  348. 


Index 


497 


Fruit-rot,  57,  134,  145,  217.  263. 
Fruit-spot,  57,   187. 
Fumago  vagans,  57,  265. 
Fungicides,  440. 

Fusarium,  20,  146,  178,  213.  249, 
257,  289,  318.  325,  331,  346, 
376,    399.   416,    418,    420,   435. 

boll-rot,  346. 

conglutinans,   172,  409. 

lini,  350. 

lycopersici.   250. 

malli,   210. 

oxysporum.  228. 

rubi,   108. 

vasinfectum.   181,   193,   201,   331, 
343. 

viote,   437. 
Fusicladium,  .35,  68,  379,  402. 

dendriticum,  147. 

effusum,  394. 
Fusicoccum,    129. 

putrefaciens,  112. 

Gall,    24,    113,   368,   402,   409,   420. 
427.        (See     also     crown-gall, 
nematode.) 
Garlic,  201. 

Gaultheria  procumbens,   113. 
Gaylussacia  resinosa,  113. 
General  diseases,  19,  354. 
Geranium,  422. 
Gibbera,   110. 

Gibberella  saubinetii,  318,  331. 
Ginseng,  24,   193. 
Gladiolus,  423. 
GlcEodes  pomigena,  55. 
GlcBOsporium,   20,   31,   44,   72,    102, 
115,    145.    148,    217,    380,    395, 
403,  430,  435. 

ampelophagum,  128. 

apocryptum,  .392. 

caulivorum.   331. 

euphorbiae.  4.35. 

medicaginis,   328. 

melongenee,    192. 

musarum,    135. 

rosse.  433. 

Aaolse,   437. 
Glomerella   cingulata,   31.   72,    112, 
395.  421,  430,  435. 


gossypii,   345. 

piperata,  217. 

psidii,   146. 
Glume  blotch,  319. 
Gnomonia,   380. 

leptostyla,  382,  403. 

ulmea,  388. 

veneta,  403. 
Gnomoniella,  380. 
Godetia,  407. 
Golden  glow,  407. 
Goldenseal,   24,    195. 
Gooseberry,    10,    117,   367. 
Granville  wilt,  253. 
Grape,  25,  87.  120. 
Graphiola-blight.    428. 
Graphiola  phoenicis.  428. 
Grass.  23,   163,  338. 
Gray-blight,   251. 
Gray-mold.  108.  174.  192,  198,  416. 

422,  426.  430.  436. 
Gray-rot.  132. 
Green-smut,   301. 
Guava,   146. 
Guignardia,   110. 

aesculi.  390. 

bidwellii.  120.  439. 

vaccinii.    110. 
Gummosis.  74,  141. 
Gymnoconia  interstitialis,   104. 
Gymnosporangium,  39,  67,  369,  376, 
383,  423. 

clavipes,   69. 
Gypsophila,  407. 

Hackberry,  379,  380,  381. 
Hairy-root,  26,  87,  162. 
Halo-blight.   299. 
Hard-rot.  423. 
Hawthorn.  379.  407,  423. 
Hazel,  369,  380,  389. 
Head-smut,  286,  309. 
Heart-rot,  361,  364,  389,  402. 
Hedera,  425. 
Helianthus,  407. 

Helicosporium   nymphsearum,   439. 
Helminthosporium,  282,  317,  402. 

carpophilum,  95. 

inconspicuum,  294,  300. 

teres,   283. 


498 


Index 


Hemileia  vastatrix,   144. 

Hemlock,   365,   367,   368,  369,  371, 

373,  379,  380. 
Hemlock,  western,  389. 
Hemp,  163,  353. 
Hendersonia,   145,  380. 
Hepatica,  96,  423. 
Herpotrichia,   380. 
Heterosporium,   425. 

echinulatum,  416. 

variable,   243. 
Hibiscus,  23,  407,  423. 

sabdariffa,    241. 
Hickory,  359,  367,  380,  381. 
Historical,  1. 

concerning  prevention,  3. 

important  events,  8. 
Holcus,  277,  278. 
Hollow-heart,    235. 
Hollow-stem,   265. 
Hollyhock,  10,  24,  423. 
Honey-locust,  381. 
Honeysuckle,  88,  407,  408. 
Hop,  87,  163,  195. 
Hordeum,  277,  278. 
Hornbeam,  359,  381. 
Horse-chestnut,  364,  367,  368,   369, 

380,  381,  390. 
Horse-radish,    195. 
Hot-water  treatment,  271,  274. 
Huckleberry,   110,   113. 
Hydnum,  367. 

erinaceus,   361. 
Hydrangea,  23,  425. 
Hydrastis,    195. 
Hymenochsete,   402. 
Hypertrophy,   1 12. 
Hypochnose,  47,  69,  73. 
Hypoderma,   380,   397. 
Hystrix,    277. 

Iberis,   407. 

Illosporium,   47. 

Impatiens,    407. 

Incense  cedar,  369,  380. 

Inga,  380. 

Injury  to  seed  by  treatment,  277. 

Insecticide,   449. 

Internal   brown-spot,    236. 

Inverted-pan   method,   461. 

Irpex,  67,  402. 


Isariopsis  griseola,   159. 
Ivy,   425. 

Japan  clover,  337. 

Java  black-rot,  420. 

Java  dry-rot,  250. 

Jelly  end-rot,  230. 

Jerusalem  artichoke,  435. 

Johnson  grass,  339. 

Jonathan-spot,  54. 

Juniper,  367,  368,  369,  380,  381. 

Junipcrus,  40,  69,  383. 

Kafir,  307. 
Kale,  163,  165. 
Kalmia  angustifolia,  113. 
Keithia,  380. 
Kernel-smut,  283,  308. 
Kernel-spot,  395. 
Knapsack  sprayer,  454. 
Knot,  147,  427.   (See  also  root-knot.) 
Kochia,   407. 
Koeleria,  277,  278. 
Kohl-rabi,    163,    165. 
Kuehneola  albida,   105. 
gossypii,  349. 

Labrella  pomi,  56. 

Lsestadia,  251. 

Larch,    367,    368,    369,    371,    373, 

380,  390. 
Large  leaf-spot,  388. 
Larkspur,  407,  426. 
Lasiodiplodia  triflorffl,  99. 
Late-blight,  174,  217,  263. 
Late-rust,  105. 
Lathryus,  407. 
Laurel,  425. 
Lavatera,   407. 
Leaf-anthracnose,    194. 
Leaf-blight,   68,  70,   134,    183.   187, 

195,    244,    250,   348,    398,   402, 

425. 
Leaf-blotch,  159,  234,  390. 
Leaf-cast,   397. 
Leaf-curl,  233,  394. 
Leaf-glaze,    191. 
Leaf-mold,  262,  416. 
Leaf-perforation,    199. 
Leaf-roll,    233,    265. 
Leaf-rot,    145. 
Leaf-scorch,    164. 


Index 


499 


Leaf-spot,  47,  68,  75,  98,  104,  114, 
119,  134,  135,  144,  145,  146, 
147,  159,  165,  173,  176,  178, 
185,  190,  191,  192,  195,  196, 
201,  214,  217,  241,  243,  244, 
245,  251,  257,  262,  295,  298, 
321,  331,  335,  338,  339,  379, 
382,  388,  391,  392,  405,  411, 
413,  415,  418,  420,  421,  422, 
424,  425,  426,  427,  428,  429, 
433,  434,  435,  439. 

Leak,   134,  234,  264. 

Leather-leaf,    113. 

Legumes,  23,  24,  321. 

Lentil,    163. 

Lentinus,  367. 

Lenzites,  367. 

Leopard-spot,    152. 

Leptospharia  coniothyrium,    105. 
leaf-blight,   319. 
sacchari,   245. 
tritici,  319. 

Leptostroma,  380. 

Leptothyrium  pomi,  380. 

Lespedeza,   337. 

Lettuce,  25,  27,  88,  196. 

Libertella,    146. 

Libocedrus,  369. 

Lichens,   144. 

Ligustrum,  407. 

Lilac,  426. 

Lily,  426. 

Lily-of-the-valley,  426. 

Limb-blight,  146. 

Lime,  23. 

Lime-sulfur,   443. 

Lime-sulfur  injury,  451. 

Lime-sulfur  wash,  445. 

Linaria,  407. 

Linden,  23,  364,  368,  369,  379,  380, 
381,   391. 

Linum,  407. 

Little-peach,  95. 

Lobelia,    407. 

Locust,  23,  361,  367,  368,  371,  379, 
380,  381,  391. 

Lolium,  277,  278. 

Lonicera,    408. 

Loose-smut,  280,  296,  315. 

Lophodermium,  380. 
brachysporum,    398.     . 


Loquat,  147. 
Lupine,  163. 
Lychnis,  407. 
Lythrum,  407. 

Macrophoma,  113,  146. 

tumefaciens,    402. 
Macrosporium,  216,  304,  380. 

herculeum,    196. 

leaf -spot,   173. 

parasiticum,  210. 

porri,  210. 

sarcinseforme,    331. 
Magnolia,  369,  379. 
Malnutrition,  173. 
Mangels,  159. 
Mango,    147. 
Mangold,  159. 

Maple,  23,  359,  361,  364,  365,  367. 
368,   369,    371,    379,    380,    381. 
392. 
Marasmius,  251. 

sacchari,   245. 
Marigold,  88. 
Marssonina,  380,  382,  403,  405. 

ochroleuca,  388. 

panattoniana,   199. 

populi,    402. 
Matthiola,    407. 
Medlar,  73. 
Melampsora,  401. 

lini,  352. 

saliciseaprae,  405. 
Melampsorella  elatina,  390. 
Melampsoridium  betulinae,  382. 
Melanose,   144. 
Melaxuma,  404. 
Melon,   178. 

Merulius  lacrymans,  374. 
Mesquite,   372. 
Microsphaera,   394. 

alni,  394,  426,  435. 

diffusa,  337. 

euphorbiae,  241. 
Microstroma,  380. 

juglandis,  395. 
Mignonette,   426. 
Migration  of  diseases,  10. 
Mildew.     (See  downy  mildew,  pow- 
dery-mildew.) 
Millet,  295. 


500 


Index 


Milo,  307. 

Mistletoe,  144,  375,  390,  395. 
Modified  hot-water  treatment,  272. 
Mold,  75,  200,  427,  428,  439.     (See 
also      gray-mold,      sooty-mold, 
black-mold,   blue-mold.) 
Monilia,  55,  75,  79,  101. 
Moniloehaetes  infuscans,  250. 
Monochetia,    380. 

desmazierii,  388. 
Moon-flower,   427. 
Morning-glory,  23,  427. 
Mosaic,  159,  186,  217,  233,  2.58,  265, 

350,   435. 
Mountain-ash,  368,  369,  380,  381. 
Mountain -laurel,    425. 
Mulberry,    23,    25,    367,    368,    369, 

372,  381,  393. 
Mushroom,  200. 
Muskmelon,  23,  25,  26,  178. 
Mustard,   163. 
Myeogone  perniciosa,  200. 
Mycosphserella,  135,  173,  338. 

citrullina,  190. 

fragarise,   132. 

gossypina,    348. 

grossularise,    114. 

leaf -spot,   114. 

pinodes,    210. 

rosigena,   433. 

rubina,   107. 

sentina,  68. 
Myxosporium,  56,  369. 

Nasturtium,  427. 

Necator  decretus,  145. 

Neck-rot,  206. 

Necrosis,  129. 

Nectarines,  90. 

Nectria,    135,    148,    251,    369,    402. 
galligena,  55,  72. 
ipomcete,  192. 

Nematode,  24,  26,  146,  159,  162, 
169,  191,  193,  195,  200,  213, 
217,  251,  259,  265,  320,  348, 
421,  435. 

Neocosmospora,  214. 

Neofabrea  mahcorticis,  44. 

Neopeckia,  380. 

Net-blotch,  283. 

Net-necrosis,  236. 

Nozzles,  458. 


Nummularia,  369. 

discreta,  44. 
Nursery-blight,   395. 
Nursery  stock,  23. 
Nut-trees,  89. 

Oak,  359,  361,  362,  364,  365,  367, 
368,    369,    371,   372,    379,   380, 
381,   394. 
Oat,  163,  280,  296. 
(Edema,   265. 
Oidium,  50,  122,  241,  420,  435,  436. 

citri-aurantii,   144. 

mespilinum,   73. 
Okra,  25,  201. 
Oleander,  88,  369,  408,  427. 
Olive,   147,  367,  369. 
Olpitrichum,    346. 
Onion,  25,  26,  201. 
Orange,  367,  368,  369. 
Orange  leaf-rust,  312. 
Orange-rust,    104. 
Orchard  grass,  280,  339. 
Orchard  trees,  371. 
Orchids,  427.    ' 
Ornamental  plants,  406. 
Orobanche,  159,  259. 

minor,   331. 
Osage  orange,  380,  394. 
Ozonium,  146,  201,  248,  323. 

omnivorum,  23,  53,  346,  372. 

root-rot,    372. 

Pacific  coast  canker,  44. 

Paeonia,  407. 

Pale-rot,  73. 

Pale-spot,    173. 

Palm,   408,  428. 

Palmetto,   368. 

Panicularia,  277. 

Panicum,  338. 

Pansy,  436. 

Parsley,   174. 

Parsnip,  88,  163,  174. 

Paspalum,    340. 

Patellina,   134. 

Pea,  22,  24,  25,  163,  210. 

Peach,  25,  79,  87,  90,  367,  369. 

Peacock  leaf-spot,   193. 

Peanut,  23,  214. 

Pear,  62,  361,  364,  368,  369,  372. 


Index 


501 


Pecan, 25, 88, 369. 379, 380, 381, 394. 
Pecky  heart-rot,  35S. 
Pec'ky-rot,  384. 
Pelargonium,  407,  422. 
Penicillium,  26,  108,  148,  193. 

digitatum,  141. 

expansum,  51,  250. 

italicum,    141. 
Pentstemon,    408. 
Peony,  24,  88,  428. 
Pepper,  23,  25,  215. 
Perforation,   405. 
Peridermium,  376,  380,  400,  401. 
Peronoplasmopara  cubensis,   178. 
Peronospora,  164,  196,  295. 

effusa,   244. 

parasitica,  171. 

schleideni,  203. 

sparsa,  433. 

trif  olio  rum,  327. 

vicise,   338. 

viola,  437. 
Persimmon,  23. 
Pestalozzia,  251,  380,  402. 

funerea,   194. 

guepini,  413. 
Petunia,  407,  429. 
Phalaris,   277. 
Phallus,    245. 
Phleospora,  380. 
Phleum,  277,  278,  341. 
Phloem-necrosis,    233. 
Phlox,  407,  408,  429. 
Pholiota,  367. 
Phoma,  20,  163,  230,  369,  380,  385. 

apiicola,    178. 

betae,    162. 

cyclamense,   421. 

cydoniae,  72. 

dahlia;,  421. 

destructive,  263. 

lingam,  169. 

persicEB,  96. 

pomi,  57. 

root-rot,    162. 

rot,  173. 
Phomopsis,  158,  250,  432. 

oitri,   144. 

kalmise,  425. 

mali,  57. 

vexans,  192,  421. 


Phoradendron,  375,  376. 
Phragmidium,  subcorticiim,  432. 
Phyllachora,   295,   33K. 

poae,  339. 

trifolii,   338. 
Phyllosticta,  217,  298,  369,  380,  390, 
439. 

acericola,  392. 

althseina,  424. 

antirrhini,  434. 

apii,  178. 

batatas,   250. 

caryae,  395. 

catalpae,   382. 

chenopodii,  244. 

chi-ysanthemi,  418. 

circumscissa,   96. 

cucurbitacearum,    190. 

hydrangese,  425. 

leaf-spot,  337. 

maculicola,  422. 

primulicola,  429. 

prunicola,  56. 

pteridis,   422. 

richardise,  413. 

shot-hole,  74,  96. 

solitaria,  37. 

straminella,  241. 

violse,  437. 
Phymatotrichum  omnivorum,  23. 
Physalis,  407. 
Physalospora,  134,  369. 

cydoniae,  42,  69,  72. 
Physanim  cinereum,  408. 
Physoderma  zeae-maydis,  292. 
Physopella  fici,  145.  394. 
Phytophthora,  20,   135. 

cactomm,  57,   194. 

infestans,  217,  263. 

omnivorum,   26. 

phaseoli,   158. 

terrestria,  143,  265. 
Pietin,  317. 
Piggotia,  380. 
Pine,  11,  22,  117,  365,  367,  368,  369, 

371,  373,  380,  381,  395. 
Pineapple,  148. 
Pineapple-disease,   245. 
Pink.  23,  163,  429. 
Pink-disease,    135. 
Pink-mold,  395. 


502 


Index 


Pink-rot,  49,  69,  210. 
Pip,   304. 
Piped  rot,  361. 
Piqueria,  407. 
Piricularia  grisea,   295. 

oryzae,  300,  339. 
Pithiness,  178. 
Plantain,   135. 

Plasmodiophora  brassicse,  168. 
Piasmopara  viticola,   125. 
Platycodon,  407. 
Plectodiscella  veneta,  102. 
Plenodomus  canker,    57. 

destruens,  248. 

fuscomaculans,  57. 
Pleospora  gramineum,  282. 

pisi,  213. 

tropceoli,  427. 
Pleurotus,  367. 
Pleuteus,  367. 

Plum,  87,  88,  90,  96,  97,  98,  367. 
Poa,  278,  338. 
Pod  black-rot,  135. 
Pod-blight,   158. 
Pod-rot,  157. 
Pod-spot,  152,  201. 
Podosphsera   leueotrichia,   50. 

oxyacanthse,  51,  77,  91. 
Pole-rot,   259. 
Pollen-bHght,  395. 
Polyporus,  361,  367. 

betulinus,  382. 

obtusus,  362. 

pergamenus,  379. 

roseus,  384. 

schweinitzii,  371. 

squamosus,  364. 

sulphureus,  361. 

versicolor,  374,  382. 
Polystictus,  368. 
Polythrineium,  328. 
Pomaceous  fruits,  31,  368,  369. 
Poplar,  88,  359,  365,  367,  368,  369, 

371,  380,  381,  401. 
Poria,  368,  402. 
Portulaca,  407. 
Potassium  sulfide,  448. 
Potato,    10,  22,  23,   24,  25,  26,  87, 

163,  217. 
Potato  spraying,  236. 

seed  disinfection,  240. 


Potentilla,  407. 
Powdery  gray-rot,  420. 
Powdery-mildew,    50,    67,    77,    91, 
101,    117,    122,    134,    159,    165, 
173,    187,    195,    213,    241,    242, 
283,    300,    307,    317,    337,    338, 
342,    376,    381,    394,    407,    412, 
420,    421,    426,    429,    431,    435, 
436,  439. 
Powdery  scab,  224. 
Power  sprayer,  456. 
Prevention  of  plant  diseases,  12,  13. 

methods,  14. 

historical,  3,  13. 
Primrose,  429. 
Primula,  407. 
Privet,  408,  430. 
Proprietary  fungicides,  449. 
Pro  thallium-blight,  422. 
Protocoronospora  nigricans,  338. 
Prune,  87. 
Prunus,  23,  369. 
Pseudomonas,    199,    294,    408,    422. 

angu latum,  257. 

aptatum,  164,  427. 

avenae,  299. 

campestris,   165. 

citri,  137. 

erodii,  422. 

glycineum,  337. 

juglandis,  404. 

lachrymans,  185. 

maculicolum,    173. 

malvacearum,  349. 

medicaginis,  324. 

phaseoH,    155. 

pisi,   213. 

pruni,  74,  79,  90,  101. 

savastanoi,    147. 

solanacearum,  159,  174,  192,  230, 
253,   260. 

stewarti,   291. 

tabacum,  257. 

translucens,  282,  319. 

tumefaciens,    87,    104,    350,    369. 
420. 

woodsii,  416. 
Pseudopeziza  medicaginis,  321. 

ribis,   115. 

trifolii,  331. 
Pseudotsuga,  368,  373. 


Index 


503 


Puccinia  allii,   210. 

antirrhini,  4.34. 

arenarisB,  429. 

asparagi,  149. 

bullata,  178. 

cannae,  413. 

chrysantbemi,  418. 

coronata,  278,  298,  .339. 

dispersa,  278,  30.5. 

fraxinata,  381. 

glumarum,  278,  313. 

graminis,  282,  310,  339,  411. 
agrostis,  278,  340. 
airse,  278. 
avensp,  277,  298. 
phleipratensis,  278,  341. 
poa;,  278. 
secalis,  277,  30.5. 
tritici,   277. 
tritici-compacti,  278. 

helianthi,  435. 

malvaceamm,  423. 

menthae,  411. 

poarum,  338. 

porri,  210. 

pringsheimiana,   119. 

purpurea,  278. 

simplex,  278,  282. 

sorghi,   294. 

tragopogonis,  242. 

triticina,   278,  312. 

vincae,  436. 

violas,  437. 
Puccinastrum  hydrangeae,  425. 
Pumpkin,  22,  24,  178. 
Punica,  407. 
Pustular-spot,   95. 
Pyrenopeziza  medicaginis,   322. 
Pyrethrum,   88,   407. 
Pythiacystis  citriophthora,    13."). 
Pythium,  163,  376. 

debaryanum,   193,  234,  328,  349. 

Quackgrass,  340. 

Quercus,  363. 

Quince,  23,  69.  88.  369. 

Radish,  22,  88,  163.  165. 
Ramularia,  132,  194,  380. 

armoracise,   196. 

primulae,  429. 


Rape,  163,  165. 

Raspberry,  22.  87.  88.  102. 

Rathay's  disease.  339. 

Ray-blight,  419. 

Razoumofskya,  375,  376,  390. 

Red-brown  root-rot,  371. 

Red -brown  rot,  365. 

Red-bud,  379. 

Red  cedar,  40. 

Red  heart-rot,  358,  361. 

Red-leaf,  69. 

Red  leaf-blight,  350. 

Red-rot,    214,    244,    371,    384,    401. 

Red-rust,  251. 

Redtop,  280.  340. 

Reseda.    407. 

Rhabdospora.   145. 

Rhamnus  cathartica.  298. 

lanceolatus,  298. 
Rheosporangium    aphanidermalus, 

163. 
Rhinotrichum.  346. 
Rhizina.  373. 

Rhizoctonia.  21.  178,  225,  328,  331, 
349. 

crocorum,  327. 

leaf-blight,    146. 
Rhizopus,  57. 

nigriran.s,  134,  191,  234,  245,  264. 
Rhododendron,   408. 

viscosum,   113. 
Rhubarb,  22.  23.  241. 
Rhytisma.  380. 

aceiinum,  392. 

punctatum,  392. 
Rice,  300. 
Richardia,  407. 
Ricinus.  40V. 
Rind-disease.  245. 
Ring-spot.  173,  245. 
Ripe-rot,   146. 
Roestelia,  39,  67,  69. 
Root-knot,   24,   146,   159,   162,    169, 
191,    193,    195,    200.    213,    217, 
251,  259,  265,  335,  348. 
Root-rot.  21.  23,  24,  51.   117,    119. 
1.30.  143.  145,  146,  162,  191,  196, 
213,245.248,289,325.327,331. 
337,    370,    402,   405,    408,   421, 
435,  437,  439. 
Root-tumor,  164. 


504 


Index 


Rose,  24,  87,  367,  407,  408,  430. 

Rose-of-Sharon,  423. 

Roselle,  94,  241,  265. 

Rosette,  57,  101,  198,  395. 

Rot,  111,  135,  148,  194,  365,  417, 
420.  (See  also  boll-rot,  brown- 
rot,  blossom-rot,  gray-rot,  soft- 
rot,  root-rot,  ripe-rot,  bitter- 
rot,  black-rot,  pink-rot,  red- 
rot,  pod-rot,  white-rot,  stem- 
rot,  wood-rot,  root-rot,  timber- 
rot.) 

Rotten-neck,  300. 

Rough-bark,  57. 

Rubber,   402. 

RuBt,  39,  67,  69,  74,  79,  96,  101,  116, 
144r  145^  149,  154,  164,  178, 
196,  2i0,  213;  2^14,  242,  2M, 
275,  282,  294,  304,  32&._  32a^ 
338,  341,  349,  352,_380^381, 
382,  ,383,  39CL_394,.  400_4&1, 
405,  409,  410,  411,  413,  414, 
418,  420,  423,  425,  427,  428, 
429,  432,  434,  435,  436,  437. 
(See  also  black-rust,  blister- 
rust,  black-stem-rust,  white- 
rust,  late-rust,  orange-rust, 
yellow-rust.) 

Rutabaga,  163,  165. 

Rye,  163,  280,  .304. 

Salsify,  25,  88,  241. 
Salvia,  407. 
Santolina,  407. 
Sap-rot,  374. 
Sapwood  rot,  364,  382. 
Sargent,  sterilizer,  462. 
Sassafras,  367,  402. 
Scab,  27,  35,  68,  74,  79,  82,  99,  132, 
142,  147,  163,  178,  283, 298, 307, 
318,  331,  394. 
Scald,  54,  110. 
Scaly-bark,   140. 
Schizanthus,  407. 
Schizophyllum,  346,  368. 

aineum,  78. 
iSclerospora,  295. 

Sclerotinia,  20,  164,  174,  178,  265, 
426,  429,  435. 

cinerea,  55,  75,  79,  101. 

fuckeliana,  132. 


libertiana,  26,  137,  158,  170,  183, 
193,  195,  196,  258. 

linhartiana,  73. 

oxycocci,  112. 

perplexa,  435. 

smilacina,    194. 

trifoliorum,  323,  329. 

tuberosa,  409. 

white  rot,  195. 
Sclerotium,  20,   174,   193,  242,  320, 
346. 

bataticola,   218,   251. 

ricini,  174. 

rolfsii,  23,  144,  146,  158,  185,  195, 
214,  215,  264,  408,  420. 
Scolecotrichimi  graniinis,  339. 
Scurf,  56,  250. 
Secale,  277,  278. 
Sedum,  407,  433. 
Seed-bed  diseases,  407. 
Seed  mold,  328. 
Seed  plat,  275. 
Septobasidium,  53,  368,  372. 

canker,  57,  69. 

pedicillatum,  57. 
Septocylindrium  rufoniaculans,  165. 

areola,  348. 
Septoglceum,   380. 
Septoria,  68,  114,  328,  381,  411,  424. 

armoraceffi,   195. 

bataticola,  251. 

chrysanthemella,  418. 

consimilis,  199. 

dianthi,  415. 

gladioli,  423. 

helianthi,  435. 

kalmicola,  425. 

lactucse,  199. 

leaf-spot,  191,  337. 

lycopersici,   262. 

petroselini,  174. 

ricini,  174. 

rubi,   104. 

sedi.  433. 
Sequoia,   .379,   381. 
Seradella,  407. 
Shadbush,  380,  381. 
Shedding,  350. 
Sheep  laurel,  113. 
Shelling,    131. 
Shoe-string  root-rot,  370.. 


Index 


505 


Shot-hole,  74,  96. 
Sida,   23. 
Silene,  407. 

Silver-leaf,  74,  96,  99,  117. 
Silver-scurf,  234. 
Slime  flux,  376. 
Slime-mold,  408. 
Slimy-rot,  114. 
Small  fruits,  102. 

Smut,  26,  201,  266,  283,  29.3,  .338, 
339,  340,  341,  349,  411.  (S(^ 
also  covered-smut,  kernel-smut, 
loose-smut,  black-smut,  cereal- 
smut.) 
kinds  of,  266. 

preventive  treatments,  268. 
seed  treatments,  270. 
Snap  dragon,  434. 
Soft-gall,  88. 
Soft  heart-rot,  382. 
Soft-rot,  26,  51,  164,  172,  179,   188, 
194,    208,    217,    241,    245,    362, 
412,   420. 
Soil  diseases,  26. 
Soil-disinfection,  460. 
Soil-rot,  249. 
Sooty-blotch,  55,  69. 
Sooty-mold,  144,  265,  408,  413. 
Sore-shin,  349. 
Sorghum,  163,  278,  307. 
Sour-rot,   144. 

Southern-blight,  23.   146,   158,   174, 
185,    193,    195,    214,    215,    242, 
264,  320,  408,  420. 
Soy  bean,  24,  337. 
Sparassis,  373. 
Spartina,  381. 
Speck, 304. 
Spelt,  310. 

Sphacelotheea    reiliana,     286,    309. 
cruenta,  308. 
sorghi,  283,  308. 
Sphseronema  finibriatum,  247. 
Sphseronemella ,   134. 
Sphseropsis    maloniin,    4L!,    69,    72, 
369. 
tumefaciens,  144. 
vincse,   436. 
Sphffirotheca  humuli,  1-34,  195,  431. 
mors-uvse,  117. 
pannosa,  91,  431. 


Spinach,  25,  163.  242. 
Spindling-sprout,  235. 
Spirea,  407. 

Spondylocladium  atrovirens,  234. 
Spongospora  subterranea,  224. 
Sporobolus,  277. 
Sporonema,  323. 
Sporotrichum  anthophilum,  417. 
Spot,j201,  257,  336.    (See  also  leaf- 
-"spot,  angular   leaf-spot,    black- 
spot,  pod-spot.) 
Spot-disease,   436. 
Spotted   blight,   304. 
Sp^ay  gun,  456. 
Spraying,   191. 
Spraying  apparatus,  452. 
Spraying    schedule,    conditions     in- 
fluencing, for  apples,  57. 
Spur-blight,  107. 
Spruce,  365,  367,  368,  369,  371,  373, 

380. 
Spurge,  435. 
Squash,  22,  23,  178. 
Stachys,  407. 

Stagonospora  carpathica,  328. 
leaf-spot,  328. 

Stalk-rot,  289. 

Steecherinum,  368. 

Stem  anthracnose,  193. 
blight,  96,  421. 
disease,  145. 

Stem-end-rot,  144,  187. 

Stem-rot,  21,  157,  213,  249.  259,  407, 
410,    416,    417,    420,    439. 

Stem-smut,  306. 

Stemphylium  cucurbitacearum,  190. 

Stereum,  368. 
purpureum,  99. 

Sterigmatocystis    nigra,     146,    210, 
260. 

Stigmatea,  381. 

Stigmonose,  416. 

Stilbella  flavida,  145. 

Stilbum,  251. 

Stinking-smut,  314. 

Stocks,  168. 

Strawberry,  25,  132. 

Streak,  159,  435,  437. 

Stripe-blight,  299,  307,  342. 

Stripe-disease,  282,  307. 

Strophostyles,  155. 

Strumella,  369. 


506 


Index 


Sudan-grass,  307. 

Sugar-beet,    24. 

Sugar-cane,  23,  24,  244. 

Sulfur-dust,  446. 

Sun-burn,  405. 

Sunflower,  163,  407,  435. 

Sunscald,  54,  159. 

Sweet-alyssum,  168. 

Sweet-gum,  381. 

Sweet-pea,   24,    163,  407,  408,  435. 

Sweet  potato,  22,  23,   24,  26,   245. 

Sycamore,  367,  369,  371,  380,  381, 

403. 
Synchytrium  endobioticum,  224. 
A'accinii,  113. 

Take-all,  317. 
Tall  oat  grass,  340. 
Taphrina,  376,  381. 

cerasi,  77. 

coerulescens,  394. 

communis,  98. 

deformans,  84. 
Tar-spot,  392. 
Taxus,  407. 
Tea,  251. 
Telanthera,  407. 
Teosinte,  283. 
Texas  root-rot,  23,  53,  69,  201,  248, 

323,   346. 
Thelephora,  368. 
Thielavia,  191,  196,  213. 

basicola,   24,    194,   251,   337,   373, 
408,  421,  435. 

root-rot,    194. 
Thielaviopsis  paradoxa,  148,  245. 
Thread-blight,  251. 
Thrombosis,  .393. 
Thyridaria,  402. 
Tilletia  horrida,  302. 

Isevis,  314. 

tritiei,   314. 
Timber,  354,  373. 
Timber-rot.  183,  265. 
Timothy,  163,  280,  .341. 
Tip-burn,  228. 
Tobacco,  22,  25,  S7,  251. 
Tomato,  22,  23,  25,  S7,  260. 
Tower,  458. 
Trametes,    368. 

pmi,  358. 


Transchelia,  423. 

punctata,   96. 
Trees,  354. 
Tree  .surgery,  376. 
Trichodemia  koningi,  251. 

-rot,  251. 
Tricholoma,  368,  372. 
Trichosphseria,  148. 

sacchari,  245. 
Triticum,  277,  278. 
Tropical  fruits,  135. 
Tropceolum,  408,  427. 
T.suga  heterophylla,  389. 
Tubercularia,    146. 
Tulip,  369,  4,36. 
Tupelo,  368. 
Turnip,  88,  163,  165. 
Tussilago,  338. 
Twig-blight,  368,  394,  398. 

Uncinula  necator,  122. 
Uredinales,  380. 
Uredo,   148. 

arachidis,  214. 
Urocystis  agropyri,  340. 

c'epulsB,  201. 

occulta,  306. 
Uromyces,  148,  329,  .338. 

appendiculatus,  1.54. 

beta,  164. 

caryophyllinus,  414. 

POEP,  339. 

striatus,  328. 
Urophlyctis,  164. 

alfalfse,  325. 

tritiei,  316. 
Ustilaginoidea  virens,  301. 
Ustilago,  295,  340. 

avena;,  296. 

crameri,  295. 

crusgalli,  338. 

hordei,  282. 

levis,  297. 

nuda,  280.  '  •.     ' 

panici-miHacei,  295. 

perennans,   340. 

shiraiana,  411. 

striseformis,  338,  340,  341. 

tritiei,   315. 

zeae,  283. 


Index 


507 


Valsa,  369. 

leucostoma,  74,  78,  86. 
Vanilla,   148. 
Vegetable  crops,  149. 
Venturia,  381. 

inaequalis,  35. 

pyrina,   68. 
Verbena,  407,  436. 
Verttiicularia,  148,  208. 

dematium,  193. 

subeffigurata,  415. 

telephii,  433. 

trichella,  425. 
Vertieillium,  192,  393. 

alboatrum,  201,^0,  412^ 

aibus,  194. 

caulophagus,  110. 

dahlise,  421. 

wilt,    194. 
Vetch,  24,  163,  338. 
Vigna,   155. 
Vinca,   407. 
Vinca  leaf-spot,  436. 
Viola,  407. 

Violet,  22,  23,  24,  408,  436. 
Virginia  creeper,  407,  439. 
Viruela,   145. 
Volutella,  20,  205,  346. 

concentrica,  412. 

dianthi,  417. 

fructi,  56. 

rot,  56,  412. 
Volvaria.  368. 


359,     361,     364, 
379,    380,    381, 


Walnut,    25,    87 
367,   368,   3f 
403- 
Wart,  224. 
Water  lUy,  439. 
Watermelon,  22,  23,  26.  178. 
Watery-rot,   144. 


Wet-butts,    260. 

Wheat,  163,  280,  310. 

White  alder,  113. 

White  cedar,  368,  369. 

White-head,  317. 

White  heart-rot,  359. 

White-rot,   132,  361,  364,  381,  383. 

White  rust,  164,  172,  173,  196, 
241,  250,  408,  427. 

White-smut,  242. 

White-spot,  328. 

White-vein,  260. 

White  wood-rot,  364. 

WUdfire,   257. 

Willow,  25,  88,  359,  364,  367,  368, 
369,    376,    379,    380,    381,   405. 

Wilt,  26,  98,  112,  135,  148,  159. 
172,  174,  181,  182,  190,  192, 
193,  201,  213,  215,  228,  230, 
249,  257,  260,  291,  323,  325. 
329,  331,  337,  343,  350,  353, 
409, 412, 416, 418, 421, 435, 437. 

Winter-blight,  265. 

Wintergreen ,    113. 

Witches-broom,   135. 

Wither-tip,   143. 

Wood-rot,  53,  78,  144. 

Xylaria,  53,  373. 

Yellow  leaf,  294,  300. 

Yellow  leaf-blotch,  322. 

Yellow-rust,  146. 

Yellow-stripe    rust,    283,    307,    313. 

Yellow-top,  328. 

Yellow  wood-rot,  391. 

Yellows,  74,  79,  91,   101,   108,   172, 

405,410,417. 
Yew,  408. 

Zygodesmus  albidus,  439. 


rmratn  library 


